Risks of 2,4-D Use to the Federally Threatened
California Red-legged Frog
(Rana aurora draytonii)
and
Alameda Whipsnake
(Masticophis lateralis euryxanthus)
Pesticide Effects Determination
Environmental Fate and Effects Division
Office of Pesticide Programs
Washington, D.C. 20460
February 20,2009
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Primary Authors:
Christine Hartless, Ph.D., Wildlife Biologist
Marie Janson, M.S., Environmental Scientist, Team Lead
Fred Jenkins, M.S., Fisheries Biologist
James Lin, Ph.D., Environmental Engineer
Anita Ullagaddi, M.S., Environmental Protection Specialist
Secondary Review:
Faruque Khan, Ph.D., Senior Scientist
Edward Odenkirchen, Ph.D., Senior Biologist
Branch Chief, Environmental Risk Assessment Branch 1
Nancy Andrews, Ph.D.
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Table of Contents
1. Executive Summary 6
2. Problem Formulation 27
2.1 Purpose 27
2.2 Scope 29
2.3 Previous Assessments 31
2.4 Stressor Source and Distribution 32
2.4.1. Environmental Fate Bridging Strategy 32
2.4.2 Physical and Chemical Properties of 2,4-D Acid 35
2.4.3 Environmental Fate Properties of 2,4-D Acid 37
2.4.4 Terrestrial Field Dissipation Study Summaries for 2,4-D 39
2.4.5 Aquatic Field Dissipation Study Summaries for 2,4-D 40
2.4.6 Forest Field Dissipation Study Summaries for 2,4-D 42
2.4.7 Environmental Transport Mechanisms 43
2.4.8 Mechanism of Action 45
2.4.9 Use Characterization 45
2.5 Assessed Species 54
2.6 Designated Critical Habitat 58
2.7 Action Area 59
2.8 Assessment Endpoints and Measures of Ecological Effect 61
2.8.1 Bridging Strategy for Toxicological Data 61
2.8.2 Assessment Endpoints 62
2.8.3 Assessment Endpoints for Designated Critical Habitat 65
2.9 Conceptual Model 67
2.9.1 Risk Hypotheses 67
2.9.2 Diagram 68
2.10 Analysis Plan 70
2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model... 71
2.10.2 Data Gaps 74
3. Exposure Assessment 74
3.1 Label Application Rates and Intervals 74
3.2 Aquatic Exposure Assessment 78
3.2.1 Surface Water Modeling Approach and Inputs for 2,4-D Acid (all
scenarios except rice and direct water application) 78
3.2.2 Surface Water Modeling Approach and Inputs for 2,4-D Ester Drift
Only and Drift+Runoff (all scenarios except rice and direct water applications)
79
3.2.3 Surface Water Modeling Approach and Inputs for Rice Scenario.. .. 81
3.2.4 Surface Water Modeling Approach and Inputs for Direct Application
Scenario 82
3.2.5 Surface Water Modeling Results and Estimated Aquatic EECs 83
3.2.6 Groundwater Modeling of 2,4-D Acid 88
3.2.7 Existing Monitoring Data 88
3.2.8 Downstream Dilution Analysis 90
3.3 Terrestrial Animal Exposure Assessment 90
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3.4 Terrestrial Plant Exposure Assessment 96
4. Effects Assessment 99
4.1 Dioxin Contaminant Toxicity to Terrestrial Organisms 101
4.2 Toxicity of 2,4-D to Aquatic Organisms 102
4.2.1 Toxicity to Freshwater Fish and Aquatic-phase Amphibians 104
4.2.2 Toxicity to Freshwater Invertebrates 106
4.2.3 Toxicity to Aquatic Plants 107
4.3 Toxicity of 2,4-D to Terrestrial Organisms 108
4.3.1 Toxicity to Birds 110
4.3.2 Toxicity to Mammals Ill
4.3.3 Toxicity to Terrestrial Invertebrates 112
4.3.4 Toxicity to Terrestrial Plants 112
4.4 Incident Database Review 113
4.4.1 Terrestrial Incidents 114
4.4.2 Plant Incidents 115
4.4.3 Aquatic Incidents 116
5. Risk Characterization 117
5.1 Risk Estimation 117
5.1.1 Exposures in the Aquatic Habitat 117
5.1.2 Exposures in the Terrestrial Habitat 126
5.1.3 Primary Constituent Elements of Designated Critical Habitat 140
5.2 Risk Description 140
5.2.1 Direct Effects 147
5.2.2 Indirect Effects (via Reductions in Prey Base) 155
5.2.3 Indirect Effects (via Habitat Effects) 160
5.2.4 Modification to Designated Critical Habitat 164
6. Uncertainties 166
6.1 Exposure Assessment Uncertainties 166
6.1.1 Maximum Use Scenario 166
6.1.2 Usage Uncertainties 166
6.1.3 Aquatic Exposure Modeling of 2,4-D 167
6.1.4 Potential Groundwater Contributions to Surface Water Chemical
Concentrations 169
6.1.5 Terrestrial Exposure Modeling of 2,4-D 170
6.1.6 Spray Drift Modeling 170
6.2 Effects Assessment Uncertainties 171
6.2.1 Age Class and Sensitivity of Effects Thresholds 171
6.2.2 Use of Surrogate Species Effects Data 172
6.2.3 Sublethal Effects 172
7. Risk Conclusions 173
8. References 181
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List of Attachments
Attachment 1: Life History of the California Red-legged Frog
Attachment 2: Baseline Status and Cumulative Effects for the California Red-
legged Frog
Attachment 3: Life History of the Alameda Whipsnake
Attachment 4: Baseline Status and Cumulative Effects for the Alameda
Whipsnake
List of Appendices
Appendix A: Multi-ai Analysis
Appendix B: Supplemental Fate Information
Appendix C: Detailed DPR PUR Data
Appendix D: PRZM/PE5 Output Files (Selected Examples)
Appendix E: Review of Dioxin Contamination
Appendix F: Ecological Effects Data
Appendix G: ECOTOX Literature
Appendix H: EIIS Incident Data
Appendix I: RQ Methods and LOC Definitions
Appendix J: T-REX Output Tables (Selected Example)
Appendix K: THERPS Output Tables (Selected Example)
Appendix L: TerrPlant Output Tables (Selected Example)
Appendix M: Supplemental Aquatic RQ Tables
Appendix N: Master Label
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1. Executive Summary
The purpose of this assessment is to evaluate potential direct and indirect effects on the
California red-legged frog (Rana aurora draytonii) (CRLF) and Alameda whipsnake
(Masticophis lateralis euryxanthus) (AW) arising from FIFRA regulatory actions
regarding use of 2,4-D on agricultural and non-agricultural sites. In addition, this
assessment evaluates whether these actions can be expected to result in modification of
designated critical habitat for the CRLF and AW. This assessment was completed in
accordance with the U.S. Fish and Wildlife Service (USFWS) and National Marine
Fisheries Service (NMFS) Endangered Species Consultation Handbook (USFWS/NMFS,
1998) and procedures outlined in the Agency's Overview Document (U.S. EPA, 2004).
The CRLF was listed as a threatened species by USFWS in 1996. The species is endemic
to California and Baja California (Mexico) and inhabits both coastal and interior
mountain ranges. The AW was listed as threatened on December 5, 1997 (62 FR 64306)
by the U.S. Fish and Wildlife Service (USFWS, 1997 and Westphal, 1998). The species
inhabits the Inner Coast Ranges in western and central Contra Costa and Alameda
counties, with occurrences additionally recorded in San Joaquin and Santa Clara counties
(USFWS, 1997, 2005, and 2006).
2,4-D (2,4-Dichlorophenoxyacetic acid) is a registered herbicide used as a plant growth
regulator that is available in several chemical forms (Table 1.1). Each of these chemical
forms has multiple registered end-use products. Target pests include a wide variety of
broadleaf weeds and aquatic weeds. Formulation types registered include emulsifiable
concentrate, granules, soluble concentrate/solid, soluble concentrate/liquid, water
dispersible granules (dry flowable), and wettable powder. Currently, labeled uses of 2,4-
D include agricultural and non-agricultural uses. Among the nationally registered uses,
soybean and cranberry are not grown in California, and 2,4-D is not labeled for use on
strawberries in California. The uses provided in Table 2.4 constitute the federal action
evaluated in this assessment.
Table I.I Chemical lor ins orcurrenllv registered 2.4-1) products
PC Code
CAS Number
Chcmic;il Nit me
030001
94-75-7
2,4D acid
030004
2702-72-9
2,4D sodium salt
030016
5742-19-8
2,4D diethanolamine (DEA) salt
030019
2008-39-1
2,4D dimethylamine (DMA) salt
030025
5742-17-6
2,4D Isoproylamine (IPA) salt
030035
32341-80-3
2,4D triisopropanolamine (TIPA) salt
030053
1929-73-3
2,4D butoxyethyl ester (BEE)
030063
1928-43-4
2,4D 2 ethylhexyl ester (EHE)
030066
94-11-1
2,4D isopropyl ester (IPE)
2,4-D is an herbicide in the phenoxy or phenoxyacetic acid family that is used post-
em ergently for selective control of broadleaf weeds. 2,4-D, a synthetic auxin herbicide,
causes disruption of plant hormone responses. Endogenous auxins are plant growth
regulator hormones. These growth regulating chemicals cause disruption of multiple
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growth processes in susceptible plants by affecting proteins in the plasma membrane,
interfering with RNA production, and changing the properties and integrity of the plasma
membrane. Excessive cell division and the resulting growth destroy the plant's vascular
transport system. Plant injuries include growth and reproduction abnormalities, especially
on new growth, but are not limited to these. The most susceptible tissues are those that
are undergoing active cell division and growth (Gibson and Liebman, 2002).
Bridging strategies to combine data across the forms of 2,4-D were established for both
the environmental fate and environmental toxicity data. These strategies follow the
strategies used in the 2,4-D Reregi strati on Eligibility Document (RED) and risk
assessments conducted for other phenoxy chemicals. All fate and toxicological values
have been converted to the acid equivalent (a.e.) based on the ratio of molecular weights.
This was done for ease of comparing fate parameters and toxicity values across the
various forms of 2,4-D. A brief summary of each strategy and rationale is given below.
More detailed discussions are presented in the respective sections of this document.
EFED proposed an environmental fate strategy in the 1988 Registration Standard for
bridging the degradation of 2,4-D esters and 2,4-D amine salts to 2,4-D acid. This
strategy follows the strategy used in the 2,4-D RED and assessments of other related
phenoxy chemicals. The bridging data provide information on the dissociation of 2,4-D
amine salts and hydrolysis of 2,4-D esters. The bridging data indicate esters of 2,4-D are
rapidly hydrolyzed in alkaline aquatic environments, soil/water slurries, and moist soils.
The weight of evidence from open literature and registrant-sponsored data indicates that
2,4-D amine salts and 2,4-D esters are not persistent under most environmental
conditions including those associated with most sustainable agricultural conditions. 2,4-
D amine salt dissociation is expected to be instantaneous (< 3 minutes) under most
environmental conditions. Although the available data on de-esterification of 2,4-D ester
may not support instantaneous conversion from the 2,4-D ester to 2,4-D acid under all
conditions, it does show 2,4-D esters in normal agriculture soil and natural water
conditions are short lived compounds (half-lives < 2.9 days). To account for the potential
for slower hydrolysis of the esters, acute aquatic exposure to the esters through
drift+runoff, as well as runoff only, was modeled as well. Chronic exposure to 2,4-D
esters was not considered since exposure is expected to be short-lived.
In concert with the fate bridging strategy, EFED established a bridging strategy for
ecological toxicity of 2,4-D. Within each of these bridged groups of 2,4-D forms, the
most sensitive toxicity endpoint was used for risk estimation. Toxicity data were not
available for all taxa and all forms. In those cases, it was assumed that toxicity would be
similar as in the other formulations in the same group.
For acute effects to aquatic animals (including aquatic-phase amphibians) and plants, data
evaluating 2,4-D acid and salts have been bridged, while the data evaluating the three
esters were separately bridged (Table 1.2). On an a.e. basis, acute toxicity to the acid and
salts is comparable; however, acute toxicity to the esters tends to be two to three orders of
magnitude higher. Since long-term exposure to the esters is not expected in aquatic
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environments, chronic risk estimation for esters, as well as the acid and salts, was
conducted using chronic toxicity data based on the acid and salts.
For terrestrial animals (including terrestrial-phase amphibians) and plants, all data
evaluating 2,4-D acid, salts, and esters have been bridged (Table 1.2). Within an
organism group, the variation in the toxicity endpoints is less than two orders of
magnitude, and for some groups, the variation is less than one order of magnitude.
Table 1.2 Summary of toxicity bridging strategies lor 2.4-1)
. 1 ciil and Salts bridged for estimating acute toxicity to aquatic organisms
and plants '
l»C'Code
Chemicid \«ime
030001
2,4D acid
030004
2,4D sodium salt
030016
2,4D diethanolamine (DEA) salt
030019
2,4D dimethylamine (DMA) salt
030025
2,4D Isoproylamine (IPA) salt
030035
2,4D triisopropanolamine (TIPA) salt
listers bridged for estimating acute toxicity to aquatic organisms
and plants
l»C Code
Clieiiiic;d Name
2,4D bulow clli\ 1 (LlLLj cblcr
030063
2,4D 2 ethylhexyl ester (EHE)
030066
2,4D isopropyl ester (IPE)
. \ cid. Salts, and listers bridged for estimating acute and chronic toxicity
to terrestrial organisms and plants
PC Code
C 'hemic;) 1 Name
030001
2,4D acid
030004
2,4D sodium salt
030016
2,4D diethanolamine (DEA) salt
030019
2,4D dimethylamine (DMA) salt
030025
2,4D Isoproylamine (IPA) salt
030035
2,4D triisopropanolamine (TIPA) salt
030053
2,4D butoxyethyl (BEE) ester
030063
2,4D 2 ethylhexyl ester (EHE)
030066
2,4D isopropyl ester (IPE)
aFor aquatic organisms, chronic toxicity data from acid and salts also used for
chronic toxicity to esters, as long-term exposure to the esters was not expected.
The effects determinations for each listed species assessed is based on a weight-of-
evidence method that relies heavily on an evaluation of risks to each taxon relevant to
assess both direct and indirect effects to the listed species and the potential for
modification of their designated critical habitats {i.e., a taxon-level approach). Since the
assessed species exist within aquatic (CRLF only) and terrestrial habitats, exposure of the
listed species, their prey, and their habitats to 2,4-D are assessed separately for the two
habitats1. Tier-II aquatic exposure models (PRZM/EXAMS) are used to estimate high-
1 The life history of the AW (Attachment 3) indicates that it occupies only terrestrial habitats and
consumes only terrestrial prey. For this reason, the AW was determined to be a solely terrestrial species and
was not included in the aquatic portion of this assessment.
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end exposures of 2,4-D in aquatic habitats resulting from runoff and spray drift from
different uses. Peak model-estimated environmental concentrations resulting from
different 2,4-D uses range from 0.08 to about 47 |ig/L with the exception of direct aquatic
applications, which result in much higher exposure estimates. These estimates are
supplemented with analysis of available California surface water monitoring data from
U.S. Geological Survey's National Water Quality Assessment (NAWQA) program and
the California Department of Pesticide Regulation (CDPR). The maximum concentration
of 2,4-D acid reported by NAWQA for California surface waters with agricultural
watersheds is 1.39 |ig a.e./L. This value is approximately 33 times less than the
maximum model-estimated environmental concentration. The maximum concentration of
2,4-D acid reported by the CDPR surface water database (2.78 |ig a.e./L) is roughly 17
times lower than the highest peak model-estimated environmental concentration.
To estimate 2,4-D exposures to terrestrial species resulting from uses involving 2,4-D
applications, the T-REX model is used for foliar and granular uses. The AgDRIFT model
is used to estimate deposition of 2,4-D on terrestrial and aquatic habitats from spray drift.
The TerrPlant model is used to estimate exposures following foliar 2,4-D applications to
terrestrial-phase CRLF and AW habitats, including plants inhabiting semi-aquatic and
dry areas. The T-HERPS model is used to allow for further characterization of dietary
exposures of terrestrial-phase amphibians and reptiles.
The effects determination assessment endpoints for the listed species include direct toxic
effects on the survival, reproduction, and growth of the listed species itself, as well as
indirect effects, such as reduction of the prey base or modification of its habitat. If
appropriate data are not available, toxicity data for birds are generally used as a surrogate
for reptiles and terrestrial-phase amphibians, and toxicity data from fish are used as a
surrogate for aquatic-phase amphibians.
Several degradates have been identified for 2,4-D in various environmental fate studies.
There is no evidence in the Reregi strati on Eligibility Decision (RED) document that any
of these degradates are of toxicological concern, and none is found in a significant
amount (>10.0%). A study in the public literature (ECOTOX) made observations of 2,4-
dichlorophenol (2,4-DCP), which may be more toxic than the parent 2,4-D to
earthworms; however, based on insignificant amounts (3.5% in an aerobic soil
metabolism study), indirect effects to the CRLF and AW via consumption of earthworms
exposed to 2,4-DCP are not of toxicological concern.
2,4-dichlorophenol (2,4-DCP) is a degradate and a key chemical intermediate in the
manufacture of 2,4-D, and the purity of this intermediate has a strong correlation to the
purity of 2,4-D acid produced from it. In the manufacture of 2,4-DCP, multiple positions
around the phenyl ring structure may be chlorinated. The desired positions for
chlorination are carbons two and four of the phenyl ring, but the reaction may yield
small quantities of compounds chlorinated at different positions. Certain combinations
of these chlorinated structures may form precursors to dioxin. However, according to
2,4-D registrants, since the 1990's the manufacturing process for 2,4-D and its chemical
intermediate, dichlorophenol, have been modified; those modifications decrease the
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chance that polychloro-dibenzodioxins (PCDD) and polychloro-furans (PCDF) are
formed during the manufacturing process. Based on EFED's risk assessment, dietary
exposure of terrestrial organisms (birds and mammals) to chlorodibenzo-p-dioxin (CDD;
dioxin) or chlorodibenzo-p-furan (CDF; furan) as contaminants in technical 2,4-D and
2,4-D ester herbicides were considered to be of no toxicological concern to piscivorous
birds and mammals.
Risk quotients (RQs) are derived as quantitative estimates of potential high-end risk.
Acute and chronic RQs are compared to the Agency's levels of concern (LOCs) to
identify instances where 2,4-D use within the action area has the potential to adversely
affect the assessed species and designated critical habitat via direct toxicity or indirect
toxicity based on direct effects to its food supply or habitat. When RQs for each
particular type of effect are below LOCs, the pesticide is determined to have "no effect"
on the listed species being assessed. Where RQs exceed LOCs, a potential to cause
adverse effects is identified, leading to a conclusion of "may affect." If a determination
is made that use of 2,4-D use "may affect" the listed species being assessed and/or its
designated critical habitat, additional information is considered to refine the potential for
exposure and effects. Best available information is used to distinguish those actions that
"may affect but not likely to adversely affect" (NLAA) from those actions that "may
affect and likely to adversely affect" (LAA) for each listed species assessed. For
designated critical habitat, distinctions are made for actions that are expected to have "no
effect" on a designated critical habitat from those actions that have a potential to result in
habitat modification.
Based on the best available information, the Agency makes a "may affect and likely to
adversely affect" determination for both the CRLF and AW from the use of 2,4-D for all
labeled uses except Citrus and Potatoes. For Citrus and Potatoes, the Agency makes a
"may affect but not likely to adversely affect" determination for both the CRLF and AW
from the use of 2,4-D.
A summary of the risk conclusions and effects determinations for the CRLF and the AW
and their critical habitats are presented in Tables 1.3 and 1.4. Use-specific
determinations for the CRLF are provided in Table 1.5, which also includes a summary
of LOC exceedances for direct effects to the CRLF for each modeled scenario and
taxonomic group. A summary of indirect effect LOC exceedances for the CRLF for each
modeled scenario and taxonomic group are provided in Table 1.6. LOC exceedances for
direct effects and indirect effects to the AW are summarized in Tables 1.7 and 1.8.
Further information on the results of the effects determination is included as part of the
Risk Description in Section 5.2. Given the LAA determination for the CRLF and AW
and potential modification of designated critical habitat for the CRLF and AW, a
description of the baseline status and cumulative effects for the CRLF is provided in
Attachment 2, and the baseline status and cumulative effects for the AW are provided in
Attachment 4.
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Table 1.3 KITccls Dclorniin;ilion Siiiniiiiirv lor (lie K fleet s of 2.4-1) on (lie CUM'' nml AW
Assessment
I'lidpoiii 1
i.nw-is
Doloi'iniiiiilioii
ISiisis I'di- Delerniin;ition
Siir\ i\ ;il. uiiiw ill.
and/or reproduction
ofCRLF
individuals
Polciili;il lor Dimi I-', fleets
LAA
Aquatic-phase (Eggs, Larvae, and Adults): Freshwater fish data used as
surrogate for CRLF.
Adult survival: Acute LOC was exceeded in the aerial forestry, tree and brush
control drift+runoff ester uses and all direct application to water scenarios.
The chance of individual effects (i.e., mortality) for freshwater fish (surrogate for
aquatic-phase CRLFs) is as high as ~1 in 1 for direct water applications.
Out of 26 incidents reported for aquatic organisms for 2,4-D acid and DMA salt,
six registered uses were reported with certainties of highly probable(2),
probable(2) and possible (2). Incidents for 2,4-D were filed on aquatic organisms
from runoff or drift. Use sites for the above incidents were reported on
home/lawn, corn, agricultural areas, rights of way/railroad, lake, pond, stream,
turf/golf course.
Growth and reproduction: Chronic LOC was not exceeded for any scenarios.
Terrestrial-phase (Juveniles and Adults) : Avian data used as surrogate for
CRLF.
Survival: Acute LOC was exceeded in all modeled scenarios except citrus and
potatoes for liquid applications. Acute LOC was exceeded in field corn, popcorn,
sweet corn, grain or forage sorghum, non-cropland, ornamental turf, grass grown
for sod, and all direct water application scenarios (ditchbanks) for granular
applications.
The chance of individual effects (i.e., mortality) for terrestrial-phase CRLF
(Avian data used as surrogate for CRLF) is as high as ~1 in 1 for direct water
applications (ditchbanks), non-cropland, forestry, tree and brush control, and
grass grown for sod applications.
Based on one incident report from runoff, 2,4-D has been implicated as being
toxic to birds with probable certainty for a use of undetermined legality.
Growth and reproduction: Dietary-based chronic RQ values exceeded the LOC
at 1 app @ 54 lb a.e./acre for aquatic weed control (ditchbanks) for liquid
applications derived from T-REX and T-HERPS modeled scenarios.
Potenthil lor Indirect I". fleets
Aquatic prey items, aquatic habitat, cover and/or primary productivity
Non-vascular aquatic plants: LOC was exceeded for all direct surface aquatic
weed control scenarios.
Vascular aquatic plants: LOC was exceeded for several acid/salt use scenarios
and all direct application to water scenarios.
Freshwater invertebrates: Acute LOC was exceeded for all direct application to
water scenarios. Based on the results of probit analysis, there is a significant
chance (> 10%) that direct applications to water (aquatic weed control ester
uses) will impact prey of the CRLF via direct effects on aquatic invertebrates as
dietary food items.
Freshwater fish: Acute LOC was exceeded for aerial forestry, tree and brush
control, and all direct application to water scenarios. Based on the results of
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Tsihle 1.3 KITeels Detenuin;ilion Siiininsirv lor (lie KITeels of 2.4-1) on (lie CUM'' nml AW
probit analysis, there is a significant chance (> 10%) that direct applications to
water will impact prey of the CRLF via direct effects on freshwater fish as
dietary food items.
Out of 26 incidents reported for aquatic organisms for 2,4-D acid and DMA
salt, 7 registered uses were reported with certainties of highly probable(2),
probable(2) and possible (2). Incidences for 2,4-D were filed on aquatic
organisms from runoff or drift. Use sites for the above incidents were reported
on home/lawn, corn, agricultural areas, rights of way/railroad, lake, pond,
stream, turf/golf course.
Terrestrial prey items, riparian habitat
Terrestrial invertebrates: Acute LOC for small insects was exceeded for all
scenarios except citrus and potatoes. Acute LOC for large insects was exceeded
for several scenarios.
Terrestrial-phase amphibians, acute toxicity: Acute LOCs were exceeded in all
T-REX and T-HERPS modeled scenarios except citrus and potatoes for liquid
applications. Acute LOC was exceeded in field corn, popcorn, sweet corn, grain
or forage sorghum, non-cropland, ornamental turf, grass grown for sod and all
direct water application scenarios (ditchbanks) for T-REX modeled granular
applications.
The chance of individual effects (i.e., mortality) for terrestrial-phase CRLF
(Avian data used as surrogate for CRLF) is as high as ~1 in 1 for direct water
applications (ditchbanks), non-cropland, forestry, tree and brush control, and
grass grown for sod applications.
Terrestrial-phase amphibians, growth and reproduction: Dietary-based chronic
RQ values exceeded the LOC at 1 app @ 54 lb a.e./acre for aquatic weed
control (ditchbank exposure) for liquid application.
Small terrestrial mammals, acute toxicity: Acute LOC was exceeded in all
modeled scenarios except citrus and potatoes for liquid applications. Acute LOC
was exceeded in field corn, popcorn, sweet corn, grain or forage sorghum, non-
cropland, ornamental turf, grass grown for sod and all direct water application
scenarios (ditchbanks) for granular applications.
Based on the results of probit analysis, there is a significant chance (> 10%) that
several of the 2,4-D uses will impact prey of the CRLF via direct effects on
mammals as dietary food items.
Based on three incident reports, 2,4-D has been implicated as being toxic to
mammals with possible and probable certainty for registered and undetermined
use legalities.
Small terrestrial mammals, growth and reproduction: For liquid applications of
2,4-D, chronic dose-based LOCs were exceeded for all application scenarios.
Chronic-dietary based RQ values exceeded the LOC for all liquid application
scenarios except potatoes and citrus.
Terrestrial plants: LOCs were exceeded for monocots for all modeled scenarios
except citrus and potatoes. LOCs were exceeded for dicots for all modeled
scenarios.
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Tsihle 1.3 KITeels Detenuin;ilion Siiininsirv lor (lie KITeels of 2.4-1) on (lie CUM'' sind AW
lliidpoiiii
inw-is
Dclcrminnlion 1
Basis for Delermin;ition
For 2,4-D, 358 incidents were reported for mostly plant damage to a wide variety
of terrestrial plants particularly from direct treatment or spray drift. 140 of these
incidents were registered uses and 143 were of unknown legality. The majority
of the reports were of possible to highly probable certainty. Other reported
incident exposures included spills, stunted growth, discoloration, runoff,
persistence in crop and carryover.
Survival, growth,
and/or reproduction
of AW individuals
LAA2
Potential for Direct Effects
Terrestrial-phase (Juveniles and Adults) : Avian data used as surrogate for AW.
Survival: Acute LOC was exceeded in all modeled scenarios except citrus and
potatoes for liquid applications. Acute LOC was exceeded in field corn, popcorn,
sweet corn, grain or forage sorghum, non-cropland, ornamental turf, grass grown
for sod, and all direct water application scenarios (ditchbanks) for granular
applications.
The chance of individual effects (i.e., mortality) for AW (Avian data used as
surrogate for AW) is as high as ~1 in 1 for direct water application (ditchbanks).
Based on one incident report 2,4-D, has been implicated as being toxic to birds
with probable certainty for an undetermined use legality.
Growth and reproduction: Dietary-based chronic RQ values exceeded the LOC
at 1 app @ 54 lb a.e./acre for aquatic weed control (ditchbanks) for liquid
application.
Poicnlial lor Indirecl I'.ITecls
Terrestrial prey items, riparian habitat
Terrestrial invertebrates: Acute LOC for small insects was exceeded for all
scenarios except citrus and potatoes. Acute LOC for large insects was exceeded
for several scenarios.
Terrestrial-phase amphibians, acute toxicity: Acute LOCs were exceeded in all
T-REX and T-HERPS modeled scenarios except citrus and potatoes for liquid
applications. Acute LOC was exceeded in field corn, popcorn, sweet corn, grain
or forage sorghum, non-cropland, ornamental turf, grass grown for sod, and all
direct water application scenarios (ditchbanks) for T-REX modeled granular
applications.
The chance of individual effects (i.e., mortality) for terrestrial-phase CRLF
(Avian data used as surrogate for CRLF) is as high as ~1 in 1 for direct water
application (ditchbanks).
Terrestrial-phase amphibians, growth and reproduction: Dietary-based chronic
RQ values exceeded the LOC at 1 app @ 54 lb a.e./acre for aquatic weed
control (ditchbank exposure) for liquid application.
Small terrestrial mammals, acute toxicity: Acute LOC was exceeded in all
modeled scenarios except citrus and potatoes for liquid applications. Acute LOC
was exceeded in field corn, popcorn, sweet corn, grain or forage sorghum, non-
cropland, ornamental turf, grass grown for sod, and all direct water application
scenarios (ditchbanks) for granular applications.
Based on the results of probit analysis, there is a significant chance (> 10%) that
several of the 2,4-D uses will impact prey of the AW via direct effects on
mammals as dietary food items.
Based on three incident reports, 2,4-D has been implicated as being toxic to
13
-------
Tsihle 1.3 KITeels Detenuin;ilion Siiininsirv lor (lie KITeels of 2.4-1) on (lie CUM'' sind AW
lliidpoiiii
inw-is
IkMcrmiiiiilion 1
ISiisis for Delermin;ition
animals with possible and probable certainty for registered and undetermined use
legalities.
Small terrestrial mammal, growth and reproduction: For liquid applications of
2,4-D, chronic dose-based LOCs were exceeded for all application scenarios.
Chronic-dietary-based RQ values exceeded the LOC for all liquid application
scenarios except potatoes and citrus.
Birds, acute toxicity: Acute LOC was exceeded in all modeled scenarios for
liquid applications. Acute LOC was exceeded in field corn, popcorn, sweet corn,
grain or forage sorghum, non-cropland, ornamental turf, grass grown for sod, and
all direct water application scenarios (ditchbank exposure) for granular
applications.
Based on the results of probit analysis, there is a significant chance (> 10%) that
all uses except potatoes and citrus uses will impact prey of the AW via direct
effects on birds as dietary food items.
Based on one incident report, 2,4-D has been implicated as being toxic to
animals with probable certainty for an undetermined use legality.
Birds, growth and reproduction: Dietary-based chronic RQ values exceeded the
LOC at 1 app @ 54 lb a.e./acre for aquatic weed control (ditchbank exposure) for
liquid application.
Terrestrial plants: LOCs were exceeded for monocots for all modeled scenarios
except citrus and potatoes. LOCs were exceeded for dicots for all modeled
scenarios.
For 2,4-D, 358 incidents were reported for mostly plant damage to a wide variety
of terrestrial plants particularly from direct treatment or spray drift. 140 of these
incidents were registered uses and 143 were of unknown legality. The majority
of the reports were of possible to highly probable certainty. Other reported
incident exposures included spills, stunted growth, discoloration, runoff,
persistence in crop and carryover.
'No effect (NE); May affect but not likely to adversely affect (NLAA); May affect and likely to adversely affect (LAA)
2 The LAA call is for all usese except Citrus and Potatoes. For both Citrus and Potatoes for both species (CRLF and AW), a
NLAA call was made by EFED. For Citrus and Potato, the LOC was exceeded for several indirect effects: (1) mammals as
prey (chronic, CRLF and AW), (2) birds as prey (acute, AW only), and (3) terrestrial plants (CRLF and AW). The reasons
for the NLAA calls are listed below:
Although the mammalian dose-based chronic LOC was exceeded for both the CRLF and the AW prey, EFED
determined that this effect would be insignificant as the potential small effect on mammal reproduction (as prey of
the CRLF and AW) would not likely impact the overall prey base. It is anticipated that any effects would be small
since the RQs only mildly exceeded the LOC.
Although the avian acute dose-based LOC was exceeded for AW prey, EFED determined that this effect was
discountable and insignificant as the predicted percentage of acute elfect was only 0.0033% of the bird population
(birds as prey items of the AW), and if even if this effect did occur, the overall prey base of the AW would likely
not be affected.
Although the terrestrial plant LOC was exceeded for both CRLF and the AW, EFED determined the effect to be
insignificant as the potential small elfect on the vegetation would likely not impact the overall habitat quality. It is
anticipated that any effects would be small as the RQs only mildly exceeded the LOC.
14
-------
Table 1.4 KITccls Dclorniin;ilion Siiiniiiiirv lor Critical llabilal Impact Analysis
Species
AsscsmiiciiI
l.mlpoinl
r.nw-is
Delerminalion 1
Basis lor Delerminalion
( Kl .1
Modilicalkiii of
aqualic-phase
I'Ci:
HM2
U n\wiri.ilpLuus l.( >Cs were e\ceeded lor iik
-------
Table 1.4 KITccts Determination Summary for Critical Habitat Impact Analysis
Species
Assessment
l.mlpninl
ll'lecls
Delerminalion 1
ISiisis lor Delerminalion
since the RQs only mildly exceeded the LOC.
Although the avian acute dose-based LOC was exceeded for AW prey, EFED determined that this effect was
discountable and insignificant as the predicted percentage of acute effect was only 0.0033% of the bird population
(birds as prey items of the AW), and if even if this effect did occur, the overall prey base of the AW would likely
not be affected.
Although the terrestrial plant LOC was exceeded for both CRLF and the AW, EFED determined the effect to be
insignificant as the potential small effect on the vegetation would likely not impact the overall habitat quality. It is
anticipated that any effects would be small as the RQs only mildly exceeded the LOC.
Table 1.5 2.4-1) I se
-specific
KITects Determinations (based on direct and indirect
effects) and Direct !¦
fleet I.OC Kxcecdance Summary for the CUM''
(herall I'llccls
Delcrminalioir
Direct I.ITccl I.OC r.xceedance
Scenario
Method1
Amialic llahilal
1 erreslri
.il llahilal
Acu le''
Chronic
Acute
Chronic
Orchard Uses
Nut Orchards,
Pistachios
G
LAA
No
No
Yes
No
Filbert
G
LAA
No
No
Yes
No
Grapes
G
LAA
No
No
Yes
No
Grapes (wine grapes)
G
LAA
No
No
Yes
No
Blueberries
G
LAA
No
No
Yes
No
Stone and Pome Fruits
G
LAA
No
No
Yes
No
Citrus
G
NLAA
No
No
No
No
A
NLAA
No
No
No
No
Agricultural - Food Crop
Uses
Field Corn, Popcorn
G
LAA
No
No
Yes
No
A
LAA
No
No
Yes
No
Sweet Corn
G
LAA
No
No
Yes
No
A
LAA
No
No
Yes
No
Potatoes
G
NLAA
No
No
No
No
A
NLAA
No
No
No
No
Sugarcane
G
LAA
No
No
Yes
No
A
LAA
No
No
Yes
No
Cereal Grains
G
LAA
No
No
Yes
No
A
LAA
No
No
Yes
No
Grain or Forage
G
LAA
No
No
Yes
No
Sorghum
A
LAA
No
No
Yes
No
Hops
G
LAA
No
No
Yes
No
A
LAA
No
No
Yes
No
Asparagus
G
LAA
No
No
Yes
No
A
LAA
No
No
Yes
No
Fallow Land and Crop
G
LAA
No
No
Yes
No
Stubble
A
LAA
No
No
Yes
No
Agricultural - Non-food Crop Uses
16
-------
Table 1.5 2.4-1) I so
-specific
K fleets Dclcrminalions (based on direct and indirect
effects) and Direct !¦
fleet LOC Kxcecdance Siiininarv lor (lie ( KIT
(herall I'llccls
Delcrminalioir
Direcl HITecl !.()( r.xcccdance
Scenario
Mclliod'
Aqualic llahilal
Terreslri
.il llahilal
Anile'
Chronic
Anile
Chronic
Established Grass
Pastures, Rangeland,
Perennial Grassland
G
LAA
No
No
Yes
No
Not in Agricultural
Production
Non-agricultural Uses
Non-cropland
G
LAA
No
No
Yes
No
A
LAA
No
No
Yes
No
Forestry
G
LAA
No
No
Yes
No
A
LAA
Yes*
No
Yes
No
Tree and Brush
G
LAA
No
No
Yes
No
Control
A
LAA
Yes*
No
Yes
No
Ornamental Turf
G
LAA
No
No
Yes
No
A
LAA
No
No
Yes
No
Grass Grown for Seed
G
LAA
No
No
Yes
No
and Sod
A
LAA
No
No
Yes
No
Direct Application to Water Uses
Rice Model
G
LAA
Yes+
No
Yes
No
A
LAA
Yes+
No
Yes
No
Aquatic Weed Control
(surface application or
subsurface injection and
ditchbank)
G
LAA
Yes+*
No
Yes
Yes
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
A
LAA
Yes+*
No
Yes
Yes
Aquatic Weed Control
G
LAA
Yes+*
No
Yes
No
(surface application and
ditchbank)
2 app @ 4 lb a.e./acre
A
LAA
Yes+*
No
Yes
No
(21-day interval)
Aquatic Weed Control
G
LAA
Yes*
No
Yes
No
(ditchbank application)
2 app @ 2 lb a.e./acre
A
LAA
Yes*
No
Yes
No
(30-day interval)
'G = ground application. A = aerial application.
2 The Effects Determination call for each individual scenario is based on results from evaluation of direct
effects (this table) and indirect effects (Table 1.6). NE = No effect; NLAA = May affect but not likely to
adversely affect; LAA = May affect and likely to adversely affect
3Yes+ = LOC exceeded for acid/salt runoff/drift scenario. Yes* = LOC exceeded for ester drift+runoff
scenario. No LOCs exceeded for any ester drift only scenarios for direct effects.
17
-------
Table 1.6 2.4-1) I so-specific In
ilired KITocl I.OC Kxcoodsinco Sunn
nsirv lor (lie CI
f.
ill
A(|iialic Plains'
A(|iialic
Imcrlchralcs'
A(|iialic-phase
Krogs and l-'ish'
1 crrcsl rial-phase
Krogs"
Small Mammals
Scenario
Method1
Non-
\ascular
Vascular
Acme
Chronic
I|l
± 't -
y: S
Xj
Acule
Chronic
Acule
Chronic
Acule
Chronic4
Orchard Uses
Nut Orchards,
Pistachios
G
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Filbert
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Grapes
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Grapes (wine grapes)
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Blueberries
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Stone and Pome Fruits
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Citrus
G
No
No
No
No
No
Yes5
No
No
No
No
No
Yes6
A
No
No
No
No
No
Yes5
No
No
No
No
No
Yes6
Agricultural - Food Crop Uses
Field Corn, Popcorn
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Sweet Corn
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Potatoes
G
No
No
No
No
No
Yes5
No
No
No
No
No
Yes6
A
No
No
No
No
No
Yes5
No
No
No
No
No
Yes6
Sugarcane
G
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Cereal Grains
G
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Grain or Forage
Sorghum
G
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Hops
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
18
-------
Table 1.6 2.4-1) I so-specific In
ilired KITecl I.OC Kxcoodsinco Sunn
nsirv lor 1 lie CI
f.
ill
Aquatic Plains'
Aquatic
Imcrlchralcs'
Aqualic-phasc
Krogs and l isli'
1 erresl rial-phase
Krogs"
Small Mammals
Scenario
Method1
Non-
\ascular
Vascular
Acule
Chronic
I|l
± 't -
y: S
Xj
Acule
Chronic
Acule
Chronic
Acule
Chronic4
Asparagus
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Fallow Land and Crop
Stubble
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Agricultural - Non-food Crop Uses
Established Grass
Pastures, Rangeland,
Perennial Grassland
Not in Agricultural
Production
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Non-agricultural Uses
Non-cropland
G
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Forestry
G
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
Yes+
No
No
Yes
Yes
Yes*
No
Yes
No
Yes
Yes
Tree and Brush
Control
G
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
Yes+
No
No
Yes
Yes
Yes*
No
Yes
No
Yes
Yes
Ornamental Turf
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Grass Grown for Seed
and Sod
G
No
No
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
A
No
Yes+
No
No
Yes
Yes
No
No
Yes
No
Yes
Yes
Direct Application to Water Uses
Rice Model
G
No
Yes+
Yes+
No
Yes
Yes
Yes+
No
Yes
No
Yes
Yes
A
No
Yes+
Yes+
No
Yes
Yes
Yes+
No
Yes
No
Yes
Yes
Aquatic Weed Control
G
Yes+*
Yes+*
Yes+*
No
Yes
NA
Yes+*
No
Yes
Yes
Yes
Yes
19
-------
Tsihle 1.6 2.4-1) I so-specific In
ilired KITecl I.OC Kxcoodsinco Sunn
nsirv lor (lie CI
f.
ill
Aquatic Plains'
Aqualic
Imcrlchralcs'
Aqualic-phasc
l;ro«»s and l-'islv'
1 erresl rial-phase
l-'rniis"
Small Mammals
Scenario
Surface application or
subsurface injection for
submersed weeds
Mel hod1
Non-
vascular
Vascular
Acme
Chronic
I|l
± 't-
y: S
Xj
Acule
Chronic
Acule
Chronic
Acule
Chronic4
A
Yes+*
Yes+*
Yes+*
No
Yes
NA
Yes+*
No
Yes
Yes
Yes
Yes
Aquatic Weed Control
Surface application for
floating and emergent
aquatic weeds
G
Yes*
Yes+*
Yes+*
No
Yes
NA
Yes+*
No
Yes
No
Yes
Yes
A
Yes*
Yes+*
Yes+*
No
Yes
NA
Yes+*
No
Yes
No
Yes
Yes
Aquatic Weed Control
Irrigation ditchbank
application
G
Yes*
Yes+*
Yes*
No
Yes
NA
Yes*
No
Yes
No
Yes
Yes
A
Yes*
Yes+*
Yes*
No
Yes
NA
Yes*
No
Yes
No
Yes
Yes
'G = ground application. A = aerial application.
2LOC exceedances based on T-HERPS refinement for small frogs.
3Yes+ = LOC exceeded for acid/salt runoff/drift scenario. Yes* = LOC exceeded for ester drift+runoff scenario. No LOCs exceeded for any ester drift only scenario.
4LOC exceedances based on dose-based chronic risks to small mammals.
5Effect determined to be insignificant as the potential small effect on the vegetation would likely not impact the overall habitat quality. It is anticipated that any effects
would be small as the RQs only mildly exceeded the LOC.
6Effect determined to be insignificant as the potential small effect on mammal reproduction (as prey of the CRLF) would not likely impact the overall prey base. It is
anticipated that any effects would be small since the RQs only mildly exceeded the LOC.
NA - Risks of aquatic weed control uses to terrestrial plants were not estimated.
20
-------
Table 1.7 2.4-1) I so
-specific
KITecIs Detenuinalions (based on direct and indirect
effects) and Direct V.
fled I.OC Kxcecdance Siiininarv lor (lie AW
0\erall 1! fleets
Delcrminalioir
Direct If foci I.OC I'.xceedaiice
Scenario
Method1
Terrestrial Habitat
Acute
Chronic
Orchard Uses
Nut Orchards,
Pistachios
G
LAA
Yes
No
Filbert
G
LAA
Yes
No
Grapes
G
LAA
Yes
No
Grapes (wine grapes)
G
LAA
Yes
No
Blueberries
G
LAA
Yes
No
Stone and Pome Fruits
G
LAA
Yes
No
Citrus
G
NLAA
No
No
A
NLAA
No
No
Agricultural - Food Crop
Uses
Field Corn, Popcorn
G
LAA
Yes
No
A
LAA
Yes
No
Sweet Corn
G
LAA
Yes
No
A
LAA
Yes
No
Potatoes
G
NLAA
No
No
A
NLAA
No
No
Sugarcane
G
LAA
Yes
No
A
LAA
Yes
No
Cereal Grains
G
LAA
Yes
No
A
LAA
Yes
No
Grain or Forage
G
LAA
Yes
No
Sorghum
A
LAA
Yes
No
Hops
G
LAA
Yes
No
A
LAA
Yes
No
Asparagus
G
LAA
Yes
No
A
LAA
Yes
No
Fallow Land and Crop
G
LAA
Yes
No
Stubble
A
LAA
Yes
No
Agricultural - Non-food Crop Uses
Established Grass
Pastures, Rangeland,
Perennial Grassland
G
LAA
Yes
No
Not in Agricultural
Production
Non-agricultural Uses
Non-cropland
G
LAA
Yes
No
A
LAA
Yes
No
Forestry
G
LAA
Yes
No
A
LAA
Yes
No
Tree and Brush Control
G
LAA
Yes
No
A
LAA
Yes
No
Ornamental Turf
G
LAA
Yes
No
A
LAA
Yes
No
Grass Grown for Seed
G
LAA
Yes
No
21
-------
Table 1.7 2.4-1) I so
effects) and Direct V.
-specific Kl'fecls Detenuinalions (based on direct and indirect
fleet I.OC Kxcecdance Summary lor the AW
(herall I'. fleets
Dclcrminalioir
Direct I.ITccl I.OC r.xcccdancc
Scenario
Method1
Terrestrial llahilal
Acute
Chronic
and Sod
A
LAA
Yes
No
Direct Application to Water Uses
Rice Model
G
LAA
Yes
No
A
LAA
Yes
No
Aquatic Weed Control
Surface application or
G
LAA
Yes
Yes
subsurface injection for
submersed weeds
A
LAA
Yes
Yes
Aquatic Weed Control
Surface application or
G
LAA
Yes
No
subsurface injection for
submersed weeds
A
LAA
Yes
No
Aquatic Weed Control
Irrigation ditchbank
application
G
LAA
Yes
No
A
LAA
Yes
No
'G = ground application. A = aerial application.
2 The Effects Determination call for each individual scenario is based on results from evaluation of direct
effects (this table) and indirect effects (Table 1.8).
NE = No effect; NLAA = May affect but not likely to adversely affect; LAA = May affect and likely to
adversely affect
22
-------
Table 1.8 2.4-1) I sc-s
pecil'ic Indirect KITcd I.OC Kx coed since Siininiarv lor (lie AW
Terrestrial
ln\erleb rales
lii
(Is
Tcrrcsl rial-phase
Krogs"
Small Mammals
Scenario
Mclliod1
Terrestrial Plants
(Acule)
Acule
Chronic
Acule
Chronic
Acule
( limine'
Orchard Uses
Nut Orchards,
Pistachios
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Filbert
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Grapes
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Grapes (wine grapes)
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Blueberries
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Stone and Pome Fruits
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Citrus
G
No
Yes4
Yes5
No
No
No
No
Yes6
A
No
Yes4
Yes5
No
No
No
No
Yes6
Agricultural - Food Crop Uses
Field Corn, Popcorn
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
A
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Sweet Corn
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
A
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Potatoes
G
No
Yes4
Yes5
No
No
No
No
Yes6
A
No
Yes4
Yes5
No
No
No
No
Yes6
Sugarcane
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
A
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Cereal Grains
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
A
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Grain or Forage
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Sorghum
A
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Hops
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
A
Yes
Yes
Yes
No
Yes
No
Yes
Yes
23
-------
Table 1.8 2.4-1) I se-s
pecil'ic Indirect KITed I.OC Kx coed since Siininiarv lor (lie AW
Terrestrial
ln\erleb rales
lii
(Is
Tcrrcsl rial-phase
Krogs"
Small Mammals
Scenario
Mclliod1
Terrestrial Plants
(Aculc)
Anile
Chronic
Acule
Chronic
Acule
( limine'
Asparagus
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
A
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Fallow Land and Crop
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Stubble
A
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Agricultural - Non-food Crop Uses
Established Grass
Pastures, Rangeland,
Perennial Grassland
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Not in Agricultural
Production
Non-agricultural Uses
Non-cropland
G
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
A
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Forestry
G
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
A
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Tree and Brush
G
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Control
A
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Ornamental Turf
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
A
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Grass Grown for Seed
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
and Sod
A
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Direct Application to Water Uses
Rice Model
G
Yes
Yes
Yes
No
Yes
No
Yes
Yes
A
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Aquatic Weed Control
G
Yes
NA
Yes
Yes
Yes
Yes
Yes
Yes
24
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Table 1.8 2.4-1) I sc-s
pccil'ic Indirect KITcd I.OC Kx coed since Siininiarv lor (lie AW
Terrestrial
ln\crlcl>ralcs
(Aculc)
lii
(Is
lerresli
lr
ial-phasc
)"s~
Small Mammals
Scenario
Mclliod1
Terrestrial Plants
Anile
Chronic
Acule
Chronic
Acule
( limine'
Surface application or
subsurface injection for
submersed weeds
A
Yes
NA
Yes
Yes
Yes
Yes
Yes
Yes
Aquatic Weed Control
Surface application for
floating and emergent
aquatic weeds
G
Yes
NA
Yes
Yes
Yes
No
Yes
Yes
A
Yes
NA
Yes
Yes
Yes
No
Yes
Yes
Aquatic Weed Control
G
Yes
NA
Yes
No
Yes
No
Yes
Yes
Irrigation ditchbank
application
A
Yes
NA
Yes
No
Yes
No
Yes
Yes
'G = ground application. A = aerial application. All applications are liquid unless otherwise specified.
2LOC exceedances based on T-HERPS refinement for small frogs.
3LOC exceedances based on dietary-based chronic risks to small mammals.
4Effect determined to be insignificant as the potential small effect on the vegetation would likely not impact the overall habitat quality. It is anticipated that any effects
would be small as the RQs only mildly exceeded the LOC.
5Effect determined to be discountable and insignificant as the predicted percentage of acute effect was only 0.0033% of the bird population (birds as prey items of the
AW), and if even if this effect did occur, the overall prey base of the AW would likely not be affected.
6Effect determined to be insignificant as the potential small effect on mammal reproduction (as prey of the AW) would not likely impact the overall prey base. It is
anticipated that any effects would be small since the RQs only mildly exceeded the LOC.
NA - Risks of aquatic weed control uses to terrestrial plants were not estimated.
25
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Based on the conclusions of this assessment, a formal consultation with the U.S. Fish and
Wildlife Service under Section 7 of the Endangered Species Act should be initiated.
When evaluating the significance of this risk assessment's direct/indirect and adverse
habitat modification effects determinations, it is important to note that pesticide
exposures and predicted risks to the listed species and its resources {i.e., food and habitat)
are not expected to be uniform across the action area. In fact, given the assumptions of
drift and downstream transport {i.e., attenuation with distance), pesticide exposure and
associated risks to the species and its resources are expected to decrease with increasing
distance away from the treated field or site of application. Evaluation of the implication
of this non-uniform distribution of risk to the species would require information and
assessment techniques that are not currently available. Examples of such information and
methodology required for this type of analysis would include the following:
Enhanced information on the density and distribution of CRLF and AW
life stages within the action area and/or applicable designated critical
habitat. This information would allow for quantitative extrapolation of the
present risk assessment's predictions of individual effects to the
proportion of the population extant within geographical areas where those
effects are predicted. Furthermore, such population information would
allow for a more comprehensive evaluation of the significance of potential
resource impairment to individuals of the assessed species.
Quantitative information on prey base requirements for the assessed
species. While existing information provides a preliminary picture of the
types of food sources utilized by the assessed species, it does not establish
minimal requirements to sustain healthy individuals at varying life stages.
Such information could be used to establish biologically relevant
thresholds of effects on the prey base, and ultimately establish
geographical limits to those effects. This information could be used
together with the density data discussed above to characterize the
likelihood of adverse effects to individuals.
Information on population responses of prey base organisms to the
pesticide. Currently, methodologies are limited to predicting exposures
and likely levels of direct mortality, growth, or reproductive impairment
immediately following exposure to the pesticide. The degree to which
repeated exposure events and the inherent demographic characteristics of
the prey population play into the extent to which prey resources may
recover is not predictable. An enhanced understanding of long-term prey
responses to pesticide exposure would allow for a more refined
determination of the magnitude and duration of resource impairment and,
together with the information described above, a more complete prediction
of effects to individual species and potential modification to critical
habitat.
26
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2. Problem Formulation
Problem formulation provides a strategic framework for the risk assessment. By
identifying the important components of the problem, it focuses the assessment on the
most relevant life history stages, habitat components, chemical properties, exposure
routes, and endpoints. The structure of this risk assessment is based on guidance
contained in U.S. EPA's Guidance for Ecological Risk Assessment (U.S. EPA, 1998), the
Services' Endangered Species Consultation Handbook (USFWS/NMFS, 1998) and is
consistent with procedures and methodology outlined in the Overview Document (U.S.
EPA, 2004) and reviewed by the U.S. Fish and Wildlife Service and National Marine
Fisheries Service (USFWS/NMFS, 2004).
2.1 Purpose
The purpose of this endangered species assessment is to evaluate potential direct and
indirect effects on individuals of the federally threatened California red-legged frog
(Rana aurora draytonii) (CRLF) and Alameda whipsnake {Masticophis lateralis
euryxanthus) (AW) arising from FIFRA regulatory actions regarding use of 2,4-D on a
variety of agricultural and non-agricultural sites as listed in Table 2.4. In addition, this
assessment evaluates whether use on these sites is expected to result in modification of
designated critical habitat for the CRLF and AW. This ecological risk assessment has
been prepared to be consistent with the settlement agreements in two court cases. This
ecological risk assessment has been prepared consistent with the settlement agreement in
Center for Biological Diversity (CBD) us. EPA et al. (Case No. 02-1580-JSW(JL)) which
addresses the CRLF and was entered in Federal District Court for the Northern District of
California on October 20, 2006. This assessment also addresses the AW for which 2,4-D
was alleged to be of concern in a separate suit (Center for Biological Diversity (CBD) us.
EPA et al. (Case No. 07-2794-JCS)).
In this assessment, direct and indirect effects to the CRLF and AW and potential
modification to designated critical habitat for the CRLF and AW are evaluated in
accordance with the methods described in the Agency's Overview Document (U.S. EPA,
2004). The effects determinations for each listed species assessed is based on a weight-
of-evidence method that relies heavily on an evaluation of risks to each relevant taxon to
assess both direct and indirect effects to the listed species and the potential for
modification of their designated critical habitats {i.e., a taxon-level approach). Screening
level methods include use of standard models such as PRZM-EXAMS, T-REX, TerrPlant
and AgDRIFT, all of which are described at length in the Overview Document.
Additional refinements include an analysis of the usage data, a spatial analysis, and use of
the T-HERPS model. Use of such information is consistent with the methodology
described in the Overview Document (U.S. EPA, 2004), which specifies that "the
assessment process may, on a case-by-case basis, incorporate additional methods,
models, and lines of evidence that EPA finds technically appropriate for risk management
objectives" (Section V, page 31 of U.S. EPA, 2004).
27
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In accordance with the Overview Document, provisions of the ESA, and the Services'
Endangered Species Consultation Handbook, the assessment of effects associated with
registrations of 2,4-D is based on an action area. The action area is the area directly or
indirectly affected by the federal action, as indicated when the Agency's Levels of
Concern (LOCs) are exceeded. It is acknowledged that the action area for a national-
level FIFRA regulatory decision associated with a use of 2,4-D may potentially involve
numerous areas throughout the United States and its territories. However, for the
purposes of this assessment, attention will be focused on relevant sections of the action
area including those geographic areas associated with locations of the CRLF and AW and
their designated critical habitats within the state of California. As part of the "effects
determination," one of the following three conclusions will be reached for each of the
assessed species in the lawsuits regarding the potential use of 2,4-D in accordance with
current labels:
"No effect";
"May affect but not likely to adversely affect"; or
"May affect and likely to adversely affect".
The CRLF and AW have designated critical habitats associated with them. Designated
critical habitat identifies specific areas that have the physical and biological features,
known as primary constituent elements (PCEs), essential to the conservation of the listed
species. The PCEs for CRLFs are aquatic and upland areas where suitable breeding and
non-breeding aquatic habitat is located, interspersed with upland foraging and dispersal
habitat. The PCEs for the AW are scrub/shrub communities with a mosaic of open and
closed canopy, woodland or annual grassland plant communities, and lands containing
rock outcrops, talus, and small mammal burrows.
If the results of initial screening-level assessment methods show no direct or indirect
effects (no LOCs are exceeded) to individuals or to the PCEs of the species' designated
critical habitat, a "no effect" determination is made for use of 2,4-D as it relates to each
species and its designated critical habitat. If, however, potential direct or indirect effects
to individuals of each species are anticipated or effects may impact the PCEs of the
designated critical habitat, a preliminary "may affect" determination is made for the
FIFRA regulatory action regarding 2,4-D.
If a determination is made that use of 2,4-D "may affect" a listed species or its designated
critical habitat, additional information is considered to refine the potential for exposure
and for effects to each species and other taxonomic groups upon which these species
depend (e.g., prey items). Additional information, including spatial analysis (to
determine the geographical proximity of the assessed species' habitat and 2,4-D use sites)
and further evaluation of the potential impact of 2,4-D on the PCEs is also used to
determine whether modification of designated critical habitat may occur. Based on the
refined information, the Agency uses the best available information to distinguish those
actions that "may affect but are not likely to adversely affect" from those actions that
"may affect and are likely to adversely affect" the assessed listed species, including
28
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potential modification to the PCEs of its designated critical habitat. This information is
presented as part of the Risk Characterization in Section 5 of this document.
The Agency believes that the analysis of direct and indirect effects to listed species
provides the basis for an analysis of potential effects on the designated critical habitat.
Because 2,4-D is expected to directly impact living organisms within the action area
(defined in Section 2.7), critical habitat analysis for 2,4-D is limited in a practical sense
to those PCEs of critical habitat that are biological or that can be reasonably linked to
biologically mediated processes (i.e., the biological resource requirements for the listed
species associated with the critical habitat or important physical aspects of the habitat that
may be reasonably influenced through biological processes). Activities that may modify
critical habitat are those that alter the PCEs and appreciably diminish the value of the
habitat. Evaluation of actions related to use of 2,4-D that may alter the PCEs of the
assessed species' critical habitat form the basis of the critical habitat impact analysis.
Actions that may affect the assessed species' designated critical habitat have been
identified by the Services and are discussed further in Section 2.6.
2.2 Scope
2,4-D is a plant growth regulator most commonly used as a herbicide for control of
broadleaf weeds. It is produced in multiple chemical forms (see Table 1.1 and Figure
2.1). After review of all the available data, EFED developed bridging strategies for both
the fate and toxicity components of the assessments. These strategies are detailed in
Section 2.4.1 and Section 2.8.1, 2,4-D is an ingredient in many agricultural and home use
products. It exists in these products as either the sole active ingredient or as an active
ingredient working in conjunction with other active ingredients. Target pests include a
wide variety of broadleaf weeds and aquatic weeds. Registered formulation types include
emulsifiable concentrate, granules, soluble concentrate/solid, water dispersible granules
(dry flowable), and wettable powder.
The end result of the EPA pesticide registration process (i.e., the FIFRA regulatory
action) is an approved product label. The label is a legal document that stipulates how
and where a given pesticide may be used. Product labels (also known as end-use labels)
describe the formulation type (e.g., liquid or granular), acceptable methods of application,
approved use sites, and any restrictions on how applications may be conducted. Thus, the
use or potential use of 2,4-D in accordance with the approved product labels for
California is "the action" relevant to this ecological risk assessment.
Although current registrations of 2,4-D allow for use nationwide, this ecological risk
assessment and effects determination addresses currently registered uses of 2,4-D in
portions of the action area that are reasonably assumed to be biologically relevant to the
CRLF and AW and their designated critical habitats. Further discussion of the action
area for the CRLF and AW and their critical habitat is provided in Section 2.7.
Bridging strategies to combine data across the forms of 2,4-D were established for both
the environmental fate and environmental toxicity data. These strategies follow the
29
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strategies used in the 2,4-D RED and risk assessments conducted for other phenoxy
chemicals. All fate and toxicological values have been converted to the acid equivalent
(a.e.) based on the ratio of molecular weights. This was done for ease of comparing fate
parameters and toxicity values across the various forms of 2,4-D. A brief summary of
each strategy and the reasoning is given below. More detailed discussions are presented
in the respective sections of this document.
EFED utilized an environmental fate strategy in the 1988 Registration Standard for
bridging the degradation of 2,4-D esters and 2,4-D amine salts to 2,4-D acid. The
bridging data provides information on the dissociation of 2,4-D amine salts and
hydrolysis of 2,4-D esters. To account for the potential for slower hydrolysis of the
esters, acute aquatic exposure to the esters through runoff and drift, as well as runoff
only, was modeled in addition to acute and chronic exposure to the acid and salts.
Chronic exposure to 2,4-D esters was not considered since exposure is expected to be
short-lived.
In concert with the fate bridging strategy, EFED established a bridging strategy for
ecological toxicity of 2,4-D. Within each of these bridged groups of 2,4-D forms, the
most sensitive toxicity endpoint was used for risk estimation. For acute effects to aquatic
animals (including aquatic-phase amphibians) and plants, data evaluating 2,4-D acid and
salts have been bridged, while the data evaluating the three esters was separately bridged.
Since long-term exposure to the esters is not expected in aquatic environments, chronic
risk estimation for esters, as well as the acid and salts, was conducted using chronic
toxicity data based on the acid and salts. For terrestrial animals (including terrestrial-
phase amphibians) and plants, all data evaluating 2,4-D acid, salts, and esters have been
bridged. Within an organism group, the variation in the toxicity endpoints is less than two
orders of magnitude, and for some groups, the variation is less than one order of
magnitude.
Several degradates were identified for 2,4-D in various environmental fate studies. There
is no evidence in the Reregi strati on Eligibility Decision (RED) document that any of
these degradates are of toxicological concern, and none of them is found in a significant
amount (>10.0%). The Metabolism Assessment Review Committee (MARC) determined
that all residues other than the parent 2,4-D are not of risk concern due to low occurrence
under environmental conditions, comparatively low toxicity, or a combination thereof
(W. Hazel andL. Taylor, TXRNo. 0052264, D293119, 12/3/03). Two studies evaluating
the degradate, 2,4-dichlorophenol (2,4-DCP), were found in open literature. 2,4-DCP was
found to be more toxic to earthworms than the parent 2,4-D acid with LCso's of 61.6
(95% CI: 41.0-92.4) [j,g/cm2 and 4.4 (95% CI: 3.2-5.9) [j,g/cm2 in a 48-hr study (Roberts
and Dorough 1984, E040531). In a second study conducted on male Swiss mice, results
indicated that the genotoxic effect of 2,4-DCP was weaker than that of 2,4-D based on
chromosomal aberrations and sperm-head abnormalities (E93505; Amer and Aly, 2001).
As with previous assessments conducted by the Agency, this assessment will be based on
the parent 2,4-D only.
30
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The Agency's risk assessments do not routinely contain an evaluation of mixtures of
active ingredients including either mixtures of multiple active ingredients in product
formulations or those in the applicator's tank. In the case of the product formulations of
active ingredients (that is, a registered product containing more than one active
ingredient), each active ingredient is subject to an individual risk assessment for
regulatory decision regarding the active ingredient on a particular use site. If effects data
are available for a formulated product containing more than one active ingredient, they
may be used qualitatively or quantitatively in accordance with the Agency's Overview
Document and the Services' Evaluation Memorandum (U.S. EPA, 2004; USFWS/NMFS,
2004).
2,4-D has registered products that contain multiple active ingredients. Analysis of the
available open literature and acute oral mammalian LD50 data for multiple active
ingredient products relative to the single active ingredient is provided in Appendix A.
Based on a review of the available studies on 2,4-D mixtures in ECOTOX, the
information presented does not indicate that 2,4-D mixtures are more toxic than the single
active ingredient. Therefore, the results of this analysis show that an assessment based on
the toxicity of the single active ingredient of 2,4-D is appropriate.
2.3 Previous Assessments
The Environmental Protection Agency issued the final Registration Eligibility Decision
(RED) for 2,4-D in June 2005. EFED's chapter, "Revised Environmental Fate and
Effects Division Revised Preliminary Risk Assessment for the 2,4-
Dichlorophenoxyacetic acid (2,4-D) Reregi strati on Eligibility Decision Document," was
finalized on October 29, 2004. EFED concluded use of 2,4-D on terrestrial sites presents
the greatest potential risks to non-target terrestrial plants, mammals, and birds, while the
use of 2,4-D for aquatic weed control presents risk to aquatic organisms and plants.
According to the Required Labeling Changes section in the final Agency RED (signed
June 30, 2005), many of the changes were related to user safety requirements, such as
PPE (personal protective equipment), REI (restricted entry interval). For use-specific
application restrictions, a setback of greater than or equal to 600 ft may be required for
the protection of drinking water. However, those requirements will not change the
outcomes of this effects determination. In addition, label rate changes for some uses and
spray drift management requirements were established as part of the Required Labeling
Changes in the RED. The spray drift management requirements were designed to limit
the conditions on droplet size, wind speed, temperature inversions, and equipment, and
they are expected to be effective in reducing the off-target spray drift.
The Agency also reviewed the registrant's endangered species assessment for 2,4-D
(Review of registrant submission entitled "Endangered Species Assessment on Non-
Target Plants Potentially at Risk from Use of 2,4-Dichlorophenoxyactic (sic) Acid in
Almonds, Rice, Strawberries, and Wheat," August 26, 2005). EFED concluded that this
assessment does not include sufficient documentation to support the findings of "no
effect" for most of the listed plant species initially identified as "potential concern" by the
co-occurrence process and the county-level resolution analysis.
31
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An endangered species assessment to determine the potential risks to 26 listed ESUs of
Pacific salmon and steelhead was done by the Field and External Affairs Division
(FEAD) in 2004 ("2,4-Dichlorophenoxyacetic Acid Analysis of Risks to Endangered and
Threatened Salmon and Steelhead," December 1, 2004). This assessment was based on
the draft 2004 EFED RED chapter. FEAD determined that the acid and salts are
practically non-toxic to slightly toxic to fish, the esters are slightly toxic to highly toxic to
fish and moderately toxic to freshwater invertebrates, and all forms are highly toxic to
vascular plants. Terrestrial uses in the Pacific Northwest pose no direct or indirect risks to
fish. However, acid and salt uses may cause indirect risks to fish via applications to rice
crops or for aquatic weed control; esters may cause acute and chronic risks directly and
indirectly via aquatic weed control uses. As a result, FEAD determined that terrestrial
crop usage would have no effect on the 26 listed ESUs of Pacific salmon and steelhead.
Rice uses may affect but are not likely to adversely affect (NLAA) 4 ESUs and would
have no effect on 22 ESUs. For aquatic weed control uses, usage information for analysis
of each ESU was deficient, but 2,4-D use may affect all 26 ESUs.
An additional endangered species assessment done by FEAD determined the potential
risks of 2,4-D EHE to one listed Pacific salmonid ESU ("2,4-D ethylhexyl ester Analysis
of Risks to Endangered and Threatened Salmon and Steelhead," May 7, 2004). It was
determined that there would be no effect on Pacific anadromous Coho salmon due to the
rapid degradation of 2,4-D EHE to the acid form.
2.4 Stressor Source and Distribution
2.4.1. Environmental Fate Bridging Strategy
The environmental fate strategy for 2,4-D is based on bridging the degradation of 2,4-D
esters and 2,4-D amine salts to 2,4-D acid (Registration Standard for 2,4-
Dichlorophenoxyacetic acid (2,4-D), 1988, 540/RS-88-115) (Figure 2.1). The bridging
data provides information on the time of dissociation of 2,4-D amine salts and rate of
hydrolysis of 2,4-D esters. There are acceptable bridging data for 2,4-D DMA, 2,4-D
IP A, 2,4-D TIP A, 2,4-D EHE, 2,4-D BEE, 2,4-D DEA, 2,4-D IPE. The sodium salt of
2,4-D is considered to be equivalent to 2,4-D acid. The bridging data indicate esters of
2,4-D are rapidly hydrolyzed in alkaline aquatic environments, soil/water slurries, and
moist soils and that the 2,4-D amine salts have been shown to dissociate rapidly in water.
Under extremely dry soil conditions, these degradation mechanisms may be inhibited to
increase persistence of 2,4-D esters. The laboratory bridging data indicate that under most
environmental conditions, 2,4-D esters and 2,4-D amine salts will degrade rapidly to
form 2,4-D acid.
32
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Figure 2.1 Schematic of Bridging Strategy of 2,4-D amine salts and 2,4-D esters to
2,4-D acid
Amine Salts of 2,4-D
2,4-D-DMA
2,4-D-IPA
2,4-D-TIPA
2,4,D-DEA
dissociation in water
Amines
Dimethylammonium
Ispropylammonium
Trii sopropylammonium
Di ethanol ammonium
Esters of 2,4-D
2,4-D EHE"
2,4-D BEE
2,4-D IPE
2,4-D Acid
/
microbial-mediated hydrolysis
alkaline-catalyzed hydrolysis
surface-catalyzed hydrolysis
Alcohols
Ethylhexanol
Butoxy ethanol
Isopropanol
Additional data submitted subsequent to establishment of the environmental fate bridging
strategy generally support the strategy for the amine salts. Direct evidence of the stability
of 2,4-D amine salts in soil and aquatic environments is difficult due to the lack of
analytical methods. Based on maximum application rates for 2,4-D amine salts (4 lb
a.e./A), 2,4-D amine salts are expected to fully dissociate in soil environments because
their theoretical concentrations in soil solution does not exceed water solubilities.
Additionally, dissociation studies indicate the time for complete dissociation is rapid (< 3
minutes). Although the analytical methods in the field studies for 2,4-D DMA were not
capable of separating and identifying 2,4-D DMA from 2,4-D acid, the most conservative
half-lives of 2,4-D DMA would be equivalent to the 2,4-D acid half-lives in field studies.
Half-lives of 2,4-D (either acid or DMA) in 2,4-DMA field studies ranged from 1.1 days
to 30.5 days with a median half-life of 5.6 days.
The de-esterification of 2,4-D esters is more difficult to generalize because it is
dependent on heterogeneous hydrolysis (microbial-mediated and surface-catalyzed
hydrolysis) and homogenous hydrolysis (alkaline catalyzed) (Schwarzenbach et
ah, 1993). The de-esterification of 2,4-D ester leads to formation of 2,4-D acid and an
associated alcohol moiety. Unlike the physical dissociation mechanism of 2,4-D amine
salts, the de-esterification of 2,4-D esters is dependent on abiotic and microbial-mediated
processes. Any environmental variable influencing microbial populations or microbial
activity could theoretically influence the persistence of the 2,4-D ester. Soil properties
including clay mineralogy, organic carbon content, temperature, and moisture content are
known to influence hydrolysis rates (Wolfe et ah, 1989 and Wolfe, 1990).
Paris et ah (1981) found the average de-esterification half-life of 2,4-D BEE in natural
waters from 31 sites with varying temperature and pH conditions (5.4 to 8.2) was 2.6
hours. They found that 2,4-D BEE degradation could be explained using second-order
33
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kinetics accounting for microbial population numbers and aqueous concentration of 2,4-
D BEE. Further research indicated second-order de-esterification rates can be predicted
through a linear regression [log kb=(0.799±0.098)* log Kow - (11.643±0.204) r2=0.94]
using the octanol: water coefficient (log Kow) as the independent variable.
Additionally, various mineral surfaces (Fe, Al, Ti oxides) have been shown to influence
hydrolysis of carboxylate esters (Torrent and Stone, 1994). Abiotic hydrolysis of 2,4-D
esters, however, is expected to be more predictable in alkaline environments. Several
field studies show phenoxy herbicide esters are more persistent under extremely dry soil
[< soil wilting point (-15 bars)] conditions (Smith and Hay den, 1980; Smith, 1972;
Smith, 1976). In moist soils [-50 to 80% field capacity (-0.3 bars)] and soil slurries,
phenoxy herbicide esters degraded rapidly (>85% degradation) during a 48-hour
incubation period. These hydrolysis studies indicate the alkyl chain configuration
affected hydrolysis rates in soils and soil slurries. The isooctyl ester of 2,4-D (2,4-D
EHE) had slower hydrolysis rates when compared to n-butyl and isopropyl esters of 2,4-
D. In field studies, Harrison et al. (1993) found no detections of 2,4-D and 2,4-DP esters
in runoff water (although detection limits were relatively high @ 20 jag a.e./L for 2,4-D
EHE) from turf sites where 2,4-DP and 2,4-D esters were applied.
Registrant-sponsored research indicates the 2,4-D esters (ethylhexyl, isopropyl,
butoxyethyl) degrade rapidly (tm< 24 hours) in soil slurries, aerobic aquatic
environments, and anaerobic, acidic aquatic environments. In terrestrial field dissipation
studies, the half-lives for 2,4-D EHE ranged from 1 to 14 days with median half-life of
2.9 days. 2,4-D BEE, applied as granules, degraded rapidly in the water column in
aquatic field dissipation studies under alkaline conditions. However, the 2,4-D BEE
residues were detected in sediment samples from Day 0 (immediately post-treatment) to
186 days post-treatment. It is unclear whether 2,4-D BEE persistence in sediment is due
to the slow release of the granule formulation or to slow de-esterification of sediment-
bound 2,4-D BEE. Available open literature and registrant-sponsored laboratory data
would suggest slow granule dissolution prolonged the persistence of 2,4-D BEE. In forest
dissipation studies, the 2,4-D EHE ester degraded slowly on foliage and in leaf litter.
The weight of evidence from open literature and registrant-sponsored data indicates that
2,4-D amine salts and 2,4-D esters are not persistent under most environmental
conditions including those associated with most sustainable agricultural conditions. 2,4-D
amine salt dissociation is expected to be instantaneous (< 3 minutes) under most
environmental conditions. Although the available data on de-esterification of 2,4-D ester
may not support instantaneous conversion from the 2,4-D ester to 2,4-D acid under all
conditions, it does show 2,4-D esters in normal agriculture soil and natural water
conditions are short-lived compounds (< 2.9 days). Under these conditions, the
environmental exposure from 2,4-D esters and 2,4-D amine salts is expected to be
minimal in both terrestrial and aquatic environments. Further analysis is required due to
2,4-D BEE persistence in sediments from aquatic field studies. Additionally, the
persistence of 2,4-D EHE on foliage and in leaf litter from registrant-submitted forest
field dissipation studies requires additional investigation. No field dissipation data
(terrestrial, forest, or aquatic) have been submitted for the amine salts, 2,4-D IP A, 2,4-D
34
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TIP A, and 2,4-D DEA, or for the esters 2,4-D BEE (aquatic field dissipation data is
available for this chemical form) and 2,4-D IPE to confirm their persistence under field
conditions.
2.4.2 Physical and Chemical Properties of 2,4-D Acid
The physical and chemical properties of 2,4-D acid are provided in Table 2.1, and the ratio
of molecular weights for all salts and esters are provided in Table 2.2. Chemical structures
are illustrated in Figure 2.2. Based on these physical and chemical properties alone, 2,4-D
acid has low potential to volatilize from soils (vapor pressure) or from water (Henry's Law
Constant). It is also unlikely to bioaccumulate in fish given the low value of the Log n-
octanol/water partition coefficient. Appendix B provides the structures and further
chemical/molecular information on 2,4-D. The molecular structure characteristics of 2,4-D
acid are important as they help understanding its mode of action at a molecular level as well
as the binding of 2,4-D acid to soil/sediment particulates.
Table 2.1 Physical and Chemical Properties of 2.4-1) acid
Common name
2,4-D acid
Chemical name
2,4-Dichlorophenoxyacetic acid
Molecular formula
C8H6CI2O3
CAS Number
94-75-7
Molecular weight
221.04
Physical state
white crystalline solid
Melting point
138 - 141 °C
Vapor pressure
1.47 x 10"7 mm Hg @25 UC
Henry' s Law
4.74 x 10"10 atm-m3/mol @ 25°C
Solubility
569 mg/L @ 20°C
Log Kow
2.81
Table 2.2 Molecular W eight Ratios (relative to 2.-1
-1) acid)
I't code
C'heinic;il 11:11110
Moleculiir Weight Riilio
030001
2,4D acid
l.uu
030004
2,4D sodium salt
1.10
030016
2,4D diethanolamine (DEA) salt
1.48
030019
2,4D dimethylamine (DMA) salt
1.20
030025
2,4D isopropylamine (IPA) salt
1.27
030035
2,4D triisopropanolamine (TIPA) salt
1.87
030053
2,4D butoxyethyl ester (BEE)
1.45
030063
2,4D 2 ethylhexyl ester (EHE)
1.51
030066
2,4D isopropyl ester (IPE)
1.19
35
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I'igiirc 2.2 Chemical structures of nil evaluated 2.4-1) forms
Acid and Sodium Salt:
PC 0300001 (2,4-D)
2,4-dichlorophenoxyacetic acid
030004 (Na)
Sodium Salt of 2,4-D
for Sodium Salt, "Na "
replaces "H".
OH
O
O
Amine Salts:
PC 030019 (DMA)
Dimethylamine Salt of 2,4-D
CI
OH
H3C^CH3
H
cr
PC 030025 (IPA)
Isopropylamine Salt of 2,4-D
O ~ [ N H,C H(C H,)2]h
PC 030035 (TIPA)
Triisopropanolamine Salt of
2,4-D
O NH+(CH CHOHCH.
PC 030016 (DEA)
Diethanolamine Salt of 2,4-D
ci
ci
o
Esters:
PC 030063 (2-EHE)
2-Ethylhexyl Ester of 2,4-D
PC 030053 (BEE)
Butoxyethyl Ester of 2,4-D
CL
CI
O
O
O
CH,
O
36
-------
Kigurc 2.2 Chemical slriiclurcs of nil evaluated 2.4-1) lornis
PC 030066 (IPE)
Isopropyl Ester of 2,4-D
ci^ci
0 y 0 CH3
0
2.4.3 Environmental Fate Properties of 2,4-D Acid
A complete database has been assembled for 2,4-D acid. Table 2.3 lists the
environmental fate properties of 2,4-D acid, along with the major and minor degradates
detected in the submitted environmental fate and transport studies. The dissipation of
2,4-D acid appears to be dependent on oxidative microbial-mediated mineralization,
photodegradation in water, and leaching. 2,4-D acid is stable to abiotic hydrolysis.
Photodegradation of 2,4-D acid was observed (ti/2=12.9 calendar days or 7.57 days of
constant light) in pH 5 buffer solution. However, the 2,4-D acid photodegradation half-
life on soil was 68 calendar days. Photodegradates of 2,4-D were identified as 1,2,4-
benezenetriol (37% of applied) and CO2 (25% of applied).
2,4-D acid is non-persistent (ti/2=6.2 days) in terrestrial environments. Soil degradates
were 2,4-DCP and 2,4-dichloroanisol (2,4-DCA). The half-life of 2,4-D acid in aerobic
aquatic environments was 15 days. Degradates in sediment/water test systems were 2,4-
dichlorophenol, 4-chlorophenol, 4-chlorophenoxyacetic acid, and chlorohydroquinone.
The major volatile degradate in soil and aquatic environments was CO2. Unidentified
radio-labeled residues were detected in non-labile soil organic matter fractions (e.g.,
fulvic acid, humic acid, and humin). Unaltered 2,4-D acid was detected in fulvic acid
fractions of the soil organic matter.
2,4-D acid was moderately persistent to persistent (ti/2=41 to 333 days) in anaerobic
aquatic laboratory studies. Intermediate degradates were 2,4-DCP, 4-chlorophenol, and
2-chlorophenol. Volatile degradates were identified as CO2, 2,4-DCA, and 4-
chlorophenol.
As noted above, several degradates were detected in the laboratory fate studies reviewed.
The degradates detected were 1,2,4-benzenetriol, 2,4-DCP, 2,4-DCA,
chlorohydroquinone (CHQ), 4-chlorophenol, volatile organics, bound residues, and
carbon dioxide. 1,2,4-benzenetriol is a photodegradate that was observed under abiotic
conditions and is less likely to occur under natural conditions where microbially-
mediated degradation occurs.
2,4-D acid has a low binding affinity (Kads < 3 and Kdes < 1) in mineral soils and
sediment. The mobility of 2,4-D acid in supplemental soil thin layer chromatography
(TLC) studies was classified as intermediately mobile (Rf=0.41) to very mobile
37
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(Rf=1.00) in "sieved" mineral soils. Aged radio-labeled residues of 2,4-D appeared to be
immobile in supplemental soil column studies.
2,4-D acid was studied in sandy loam, sand, silty clay loam, and loam soil. Freundlich
Kads values were 0.17 for the sandy loam soil, 0.36 for the sand soil, 0.52 for the silty
clay loam soil, and 0.28 for the loam soil. Corresponding Koc values were 70, 76, 59 and
117 mL/g. 2,4-DCP had Freundlich Kads values were 2.0 for the sandy loam soil, 1.7 for
the sand soil, 3.3 for the silty clay loam soil, and 2.9 for the loam soil. Corresponding
Koc values were 821, 368, 374 and 1204 mL/g. 2,4-DCA had Freundlich Kads values of
1.6 for the sandy loam soil, 2.1 for the sand soil, 5.4 for the silty clay loam soil, and 3.5
for the loam soil. Corresponding Koc values were 667, 436, 616 and 1442 mL/g.
Tsihle 2.3 Sum 111:1 r\ of 2.4-1) Acid Knvironinenlnl l-nle Properties
Sliulj
Value
Mii.jor IK'iir;i(l;ik's
Minor Ih'^rutlulcs
MRU)
Sliulj Siiiius
Hydrolysis
Stable
410073-01
Acceptable
Direct Aqueous
Photolysis
ti/2 = 12.98 days
1,2,4-benzenetriol (37%
of applied) and C02 (25%
of applied)
411253-06
Acceptable
Soil Photolysis
ti/2 = 68 days
C02 (5% of applied)
411253-05
Acceptable
Aerobic Soil
Metabolism
ti/2 ranged from 1.44 to 12.4
days
2,4-DCP (3.5%) and 2,4-
DCA (2.8%)
00116625
431675-01
Acceptable
Anaerobic
Aquatic
Metabolism
ti/2 = 41 to 333 days
2,4-DCP, 4-chlorophenol,
and 2-chlorophenol
433560-01, 415579-01
Acceptable
Aerobic
Aquatic
Metabolism
ti/2 = 15 days
2,4-DCP, 4-chlorophenol,
4-chlorophenoxyacetic
acid, and
chlorohydroquinone
420453-01, 429792-01,
441886-01
Acceptable
Adsorption/
Desorption
Kd-ads / Kd-des
(mL/g)
Koc- ads / Koc-des
(mL/g)
Freundlich Kd values were
0.17 for the sandy loam soil,
0.36 for the sand soil, 0.52
for the silty clay loam soil,
and 0.28 for the loam soil.
Corresponding Koc values
were 70, 76, 59, and 117
mL/g.
420453-02, 00112937,
441179-01
Acceptable
Terrestrial
Field
Dissipation
The first-order half-lives
ranged from 1.1 days to 42.5
days with a median half-life
of 6.1 days
439147-01,437624-01,
437624-02, 435146-01,
435334-01,438640-01,
435928-01,437624-03,
437624-04, 436406-01,
438317-02, 438727-03,
438491-02, 438317-01,
437052-02
Acceptable
Aquatic Field
Estimated dissipation half
439083-02, 439547-01,
Acceptable
38
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Table 2.3 Summary of 2.4-1) Acid Knvironmenlal Kale Properties
Sludj
Value
M;i.jor Doui'iidiilos
Minor /h'^rutlulcs
MRU)
Siuclj Siiiius
Dissipation
lives of 20.7 and 2.7 days in
water from the North
Carolina pond after the first
and second applications, 14
days and 6.1 days in water
from a North Dakota pond
after the first and second
applications, and 1.0 day in
water from the Louisiana rice
paddy after the single
application
434916-01
2.4.4 Terrestrial Field Dissipation Study Summaries for 2,4-D
In order to address the field behavior of 2,4-D under actual use conditions, 15 terrestrial
field dissipation studies were conducted using 2,4-D DMA, and 15 terrestrial field
dissipation studies were conducted using 2,4-D EHE. No terrestrial field dissipation
studies were conducted using 2,4-D IP A, 2,4-D TIP A, 2,4-D DEA, 2,4-D BEE, or 2,4-D
IPE. Field studies were conducted using 2,4-D DMA on bareground, pasture, corn, turf,
and wheat. Field studies were conducted using 2,4-D EHE on bareground, pasture, corn,
turf, and wheat to represent major uses of 2,4-D. In addition, three aquatic field
dissipation studies and one forest field dissipation study were conducted using 2,4-D
DMA, while two forest field dissipation studies were conducted using 2,4-D EHE. An
additional aquatic dissipation study was conducted using 2,4-D BEE.
The registrant conducted a total of 30 terrestrial field dissipation studies in CA, CO, NC,
ND, NE, OH, and TX on bareground plots as well as plots cropped to corn, pasture, turf,
and wheat. The first-order 2,4-D acid half-lives ranged from 1.1 days to 42.5 days with a
median half-life of 6.1 days. These half-lives reflect dissipation from the surface soil
layer (0 to 6 inches) and do not include residues that have leached below the surface
layer. The data indicate a rapid to moderately rapid dissipation rate for 2,4-D acid.
Dissipation rates for 2,4-D degradation products (2,4-DCP and 2,4-DCA) were not
estimated because of their sporadic occurrence patterns in surface soils. The results of
this study are also consistent with half-lives from laboratory studies. Results from
laboratory studies indicate rapid to moderately rapid degradation under aerobic soil
conditions with half-lives ranging from 1.4 days to 12.4 days with a median half-life of
2.9 days.
EFED believes that little information on the behavior of 2,4-D DMA and 2,4-D EHE will
be gained from the submission of additional field dissipation studies. Sufficient data has
been presented that demonstrates 2,4-D has a moderate to high potential for soil mobility
under normal agricultural practices. 2,4-D residues were detected below a depth of 18
inches in eleven of the terrestrial field dissipation studies reviewed and was detected
below 30 inches in five studies (MRID 43914701, 43762402, 43831703, 43849101, and
39
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43872702). Leaching appears to be a route of dissipation when precipitation or
irrigation exceeds evapotranspiration demands. NAWQA data reported maximum 2,4-D
concentrations in surface and groundwater of 15 and 14.8 jag a.e./L, respectively. It
should be noted that the next highest concentration detected in the NAWQA groundwater
data is 4.54 jag a.e./L while the highest concentration detected in drinking water derived
from groundwater reported in the US EPA Office of Water's NCOD is 8 jag a.e./L.
EFED conducted comparative analysis of all 2,4-D acid half-lives estimated from the 30
field dissipation studies reviewed. Comparisons were done between granular
formulations versus concentrates, between bare soil and cropped fields, and between the
2,4-D acid half lives from studies conducted with 2,4-D DMA and 2,4-D EHE forms
separately. Each analysis is discussed below and all half-lives are for 2,4-D acid:
Comparison of descriptive statistics for the granular versus concentrate half-lives
suggests that the granular applications will result in longer half-lives than the
concentrate forms. The granular half-lives ranged from a maximum of 24.6 days
to a minimum of 5.1 days with a median half-life of 11.9 days, while the
concentrate form had half-lives ranging from a maximum of 42.5 days to a
minimum of 1.1 days with a median half-life of 5.5 days. The median granular
half-life is approximately twice the concentrate form suggesting a longer half-life.
Comparison of descriptive statistics for the bare soil half-lives versus cropped plot
half-lives suggests that there is no appreciable difference in dissipation rates
based on the presence of plants (including turf). The bare soil half-lives ranged
from a maximum of 42.5 days to a minimum of 1.1 days with a median half-life
of 5.1 days, while the cropped half-lives ranged from a maximum of 39.2 days to
a minimum of 2.2 days with a median half-life of 7.8 days.
Comparison of descriptive statistics for the 2,4-D acid half lives determined when
applying 2,4-D DMA versus the applying 2,4-D EHE chemical form suggests that
there is no appreciable difference in dissipation rates between 2,4-D DMA and
2,4-D EHE forms. The 2,4-D acid half-lives from the 2,4-D DMA studies ranged
from a maximum of 30.5 days to a minimum of 1.1 days with a median half-life
of 5.6 days, while the 2,4-D acid half lives from studies using the 2,4-D EHE
form had half-lives ranging from a maximum of 42.5 days to a minimum of 1.2
days with a median half-life of 6.2 days.
2.4.5 Aquatic Field Dissipation Study Summaries for 2,4-D
In order to address the behavior of 2,4-D in aquatic water systems a series of aquatic field
dissipation studies were conducted. Three studies were conducted using 2,4-D DMA
while a fourth study was conducted using 2,4-D BEE. Two additional dispersion and
dissipation studies using 2,4-D DMA were also submitted.
In three supplemental aquatic field dissipation studies conducted in North Dakota, North
Carolina, and Louisiana, 2,4-D DMA immediately converted to 2,4-D acid. EFED
40
-------
estimated a 2,4-D half-life in water from the North Carolina pond after the first
application of 20.4 days and after the second application of 2.7 days. EFED estimated a
half-life of 2,4-D in water from the North Dakota pond after the first application of 14.0
days and after the second application of 6.1 days. EFED estimated a half life in water
from the Louisiana rice paddy after the single application of 1.0 day. The aquatic
dissipation studies for 2,4-D DMA confirm that 2,4-D DMA quickly converts to 2,4-D
acid and dissipates rapidly from the water column.
In addition, the 2,4-D Task Force submitted two dispersion and dissipation studies for the
application of 2,4-D DMA to control aquatic weeds. The first study was for the surface
application of 2,4-D DMA to a lake in Lake Woodruff, Florida for the control of water
hyacinth. The review of the study is currently pending. However, a preliminary
summary of the results is presented below along with the previously reviewed studies. In
this study, 2,4-D DMA was surface applied at a rate of 3.8 lb a.e./acre to approximately
3.9 acres within an overall water body of 2200 acres. The highest single concentration
detected was 270 |ig a.e./L at three hours after application within the application area.
The highest concentration detected outside the application area was 122 |ig a.e./L
approximately 18.4 meters from the application area. The study authors calculated a
dissipation half-life for 2,4-D from the application area of 2.3 days, however, this half-
life does not distinguish between degradation, sorption, and transport away from the
application area.
In the second dispersion and dissipation study, 2,4-D DMA was applied by subsurface
injection to a water body located in Green Lake, Minnesota for the control of Eurasian
water milfoil. 2,4-D was applied as 2,4-D DMA by subsurface injection at a rate of 10.8
pounds of acid equivalent per acre-foot (lb a.e./acre-foot) to achieve a target
concentration in the application area of 4 parts per million (ppm). 2,4-D DMA was
applied on September 11, 2002 to approximately 4.5 acres with a dense stand of Eurasian
water milfoil. Green Lake is located in Chisago County, Minnesota. It is a 1714 acre
"low-flow" lake. The study authors report that the location, test site (static to low-flow
lake) and application method were chosen because they represent a typical use pattern for
2,4-D DMA. The highest single concentration detected was 13,193 |ig a.e./L at one hour
after application within the application area. The highest concentration detected outside
the application area was 3374 jag a.e./L approximately immediately outside the
application area. The furthest detection of 2,4-D outside the application area greater than
the MCL was on day 11 at 82.3 jag a.e./L while the furthest concentration detected above
the LOQ was 1605 meters. The study authors calculated a dissipation half life for 2,4-D
from the application area of 3.23 days; however, this half-life does not distinguish
between degradation, sorption, and transport away from the application area.
In a supplemental study, the aquatic field dissipation of 2,4-D BEE was studied in ponds
in North Carolina, Minnesota, and Washington. A single aquatic field dissipation study
conducted on three separate ponds was submitted for 2,4-D BEE. All three ponds used in
this study were alkaline (pH ranged from 7.9 to 8.1). As noted in the environmental fate
assessment, the esters of 2,4-D convert to 2,4-D acid by abiotic hydrolysis; however, the
rate is pH dependent. 2,4-D BEE was detected in water and sediment in these studies;
41
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however, 2,4-D BEE was not present for a sufficient time to estimate half-lives in water.
Half-lives for 2,4-D acid in water from the three ponds ranged from 2 to 40 days, while
the half-lives of 2,4-D acid in sediment ranged from 5 to 29 days. EFED also estimated
half-lives in sediment from the North Carolina pond of 9.6 days for 2,4-D BEE and 80.5
days for the degradate 2,4-DCP. Data from this aquatic field dissipation study in granular
form in the North Carolina pond suggest that the granular formulation of BEE is more
persistent than the DMA chemical form. The maximum concentration detected of 2,4-D
acid in water was 2,700 jag a.e./L at 15 days post-treatment from the North Carolina site.
Additional data on the behavior of 2,4-D BEE in aquatic systems was submitted in a
supplemental anaerobic aquatic metabolism study. Radio-labeled 2,4-D BEE, at 7 ng/g,
had a first-order half-life of 14.4 hours in a strongly acidic, rice paddy water and
sediment test system. The major degradate of 2,4-D BEE was 2,4-D. The degradate 2,4-
D was stable during a 12 month incubation period. Unidentified residues were also
detected (<4% of applied) in sediment and water samples. The reported results suggest
that 2,4-D BEE should not persist in acidic, anaerobic aquatic environments.
Finally, four aquatic field dissipation studies were previously submitted and reviewed,
which provide additional information on the behavior of 2,4-D in field environments.
These studies were submitted and reviewed previously as part of the Registration
Standard issued in 1988. These studies provided supplemental data on the aquatic field
dissipation and accumulation in non-target organisms of 2,4-D DMA and 2,4-D BEE.
2,4-D acid, formulated as Weedar 64 and applied at 20 and 40 lb/A, had a field
dissipation half-life of < 3 days in reservoirs at Banks Lake, Washington and Fort Cobb,
Oklahoma. In the Rock Ranch canal and the Cherry Creek lateral, 2,4-D had half-life of
< 133 minutes for locations 7 miles downstream from the application site. In the
Guntersville reservoir on the Tennessee River amended with 2,4-D DMA at 20 and 40
lb/A, the water concentration of 2,4-D was 4.8 [j,g/mL at 8 hours post-treatment and
declined to <0.11 [j.g/mL at 6 months post-treatment. In two ponds, a bayou, a lagoon,
and a lake (located in Louisiana) amended with 2,4-D DMA at 1, 4, or 10 lb/A, 2,4-D
"residues" had a dissipation half-life of < 14 days. The concentration of 2,4-D residues at
7 days post-treatment ranged from 8 to 999 [j.g/L and then declined to 1 to 45 [j,g/L at 28
days post-treatment.
2.4.6 Forest Field Dissipation Study Summaries for 2,4-D
In order to address the behavior of 2,4-D in forest systems, two forest field dissipation
studies were conducted. One study was conducted using 2,4-D DMA, while the second
was conducted using 2,4-D EHE. In a supplemental forest field dissipation study in
Oregon, 2,4-D DMA also converted rapidly to 2,4-D acid. Parent 2,4-D DMA broadcast
applied as a spray (by helicopter) at a nominal rate of 4.0 lb a.e./A onto a forest plot of
loam soil planted with fir trees dissipated with EFED-estimated half-lives for 2,4-D acid
using linear regression of log transformed data (mean concentrations of data from 0 to 6
inches collected through 398 days) of 59 days (r2 = 0.74) in exposed soil, 68 days (r2 =
0.63) in protected soil, 42 days (r2 = 0.81) on foliage, and 72 days (r2 = 0.82) on leaf
litter. In a supplemental forest field dissipation study in Georgia, parent 2,4-D EHE was
42
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broadcast applied as a spray at a nominal rate of 4.0 lb a.e./A to a forested plot of sandy
clay loam soil in Georgia. EFED attempted to estimate half-lives of 2,4-D and 2,4-D
EHE in soil (exposed and protected) using linear regression of log transformed data
(mean concentrations of data from 0 to 6 inches collected through 398 days); however,
the half-lives of 2,4-D acid in soil are questionable due to variability in the data. EFED
estimated half-lives in foliage for 2,4-D of 32.5 days (r2 = 0.80) and for 2,4-D EHE of
32.7 days (r2 = 0.51). EFED estimated half-lives in leaf litter for 2,4-D of 51.7 days (r2 =
0.55) and for 2,4-D EHE of 50.5 days (r2 = 0.53).
A series of fate studies were submitted for the moieties of various chemical forms of 2,4-
D. These moieties included dimethylamine (DMA), isopropylamine (IPA),
triisopropylamine (TIPA), diethanolamine (DEA), ethylhexyl ester (EHE), butoxyethanol
(BEE), and isopropanol (IPE). Fate studies were conducted for aerobic soil metabolism,
aerobic aquatic metabolism, and anaerobic aquatic metabolism. The studies indicated
that under aerobic soil conditions DMA degraded with half-lives between 4 and 14 days,
EHE degraded with a half-life of 5.3 hours, IPA degraded with half-lives between 11.8 to
18.2 hours, TIPA degraded with half-lives between 0.9 to 1.6 days, BEE degraded with
half-lives between 13.3 to 35.5 hours, DEA degraded with a half-life of 1.7 days, and IPE
degraded with half-life of 0.9 hours. The studies indicated that under aerobic aquatic
conditions, DMA degraded with a half-life of 2.8 days, IPA degraded with a half-life of
21.6 hours, TIPA degraded with a half-life of 14.3 days, BEE degraded with half-lives
between 0.6 to 3.4 days, DEA degraded with a half-life of 5.8 days, and IPE degraded
with a half-life of 13 hours. Finally, the studies indicated that under anaerobic aquatic
conditions DMA degraded with a half-life of 1732 days, EHE degraded with a half-life of
15.3 days, IPA degraded with a half-life of 408 days, TIPA degraded with a half-life of
15.3 days, BEE degraded with a half-life of 1.4 days, DEA degraded with a half-life of
10.9 days, and IPE degraded with a half-life of 14.55 days. These data suggest that
degradation products of 2,4-D moieties should not accumulate under normal agricultural
conditions.
2.4.7 Environmental Transport Mechanisms
Potential transport mechanisms include pesticide surface water runoff, spray drift, and
secondary drift of volatilized or soil-bound residues leading to deposition onto nearby or
more distant ecosystems. Surface water runoff and spray drift are expected to be the
major routes of exposure for 2,4-D.
In general, deposition of drifting or volatilized pesticides is expected to be greatest close
to the site of application. Computer models of spray drift (AgDRIFT and/or AGDISP)
are used to determine potential exposures to aquatic and terrestrial organisms via spray
drift.
The processes by which pesticides may be transported away from the target site include
spray drift at the time of application and volatilization. Spray drift has been well studied
and the Agency spray drift exposure assessment is considered in EFED's risk assessment
models. However, transport after volatilization is not as well studied and the impact of
43
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the potential transport of 2,4-D esters away from the target site is not included
quantitatively in this assessment.
Much evidence reported in open literature suggests concern for impact to non-target
organisms due to drift and volatilization of the ester forms of the phenoxy herbicides.
The state of Florida passed the Organo-Auxin Herbicide Rule which restricts the use of
highly volatile esters based on concerns over volatility; however, these banned esters are
high volatility esters and do not include 2,4-D EHE and BEE (email from Dale Dubberly,
Florida Department of Agriculture and Consumer Services, dated August 12, 2003).
Other states have similarly banned or restricted the use of certain phenoxy herbicides
including esters, while other states have issued warnings on the use of phenoxy
herbicides, particularly under dry moisture conditions and warmer temperatures
(Feitshans, 1999). A March 2008 memo from the Pesticide Registration and Evaluation
Committee of DPR titled "Prioritization and status of active ingredients for risk
characterization: Report 50" (http://www.cdpr.ca.gov/docs/risk/priot.pdf). lists 2,4D salt
and ester compounds as Toxic Air Contaminants (TACs), and places them in high priority
for review and completion of a risk assessment. Finally, the Association of American
Pesticide Control Officials (AAPCO) report in the 1999 Pesticide Enforcement Survey
(http://aapco.ceris.perdue.edu/doc/survevs/drift99.htmn that 2,4-D is the most commonly
confirmed active ingredient by state agencies as regards to drift complaints. However the
survey does not distinguish between 2,4-D chemical forms, does not differentiate
between drift and volatility, and indicates that the most common confirmation technique
is visual examination and residue confirmation.
Data collected in the 1960s and 1970s, and summarized in Majewski and Capel (1995),
indicate that 2,4-D has been detected in rainwater samples at concentrations between 50
nanograms per liter (ng/L) and 204,000 ng/L, while 2,4-D was detected in air samples at
concentrations between 1.15 nanograms per gram (ng/g) and 1410 ng/g. Majewski and
Capel noted that the higher concentrations were infrequently detected, and the authors
also noted that the high detections were located near areas where pesticides were applied
and may have resulted from unusual conditions. More recent data reported by Anderson
et al. (2002) on water and rainfall samples in a wetland environment in Alberta, Canada
indicate that 2,4-D was one of the most frequently detected pesticides in rainfall samples
with a frequency of detection of 65%. However, concentrations did not exceed 1 (J,g/L. In
a study conducted in southern Manitoba by Rawn et al. (1999), 2,4-D was detected in
rainfall at concentrations less than 1 [j.g/L and was detected in air as both vapor and
particle phase at a maximum concentration of 3500 picograms per cubic meter (pg/m3).
Both rainfall and air detections were closely associated with local use; however, the
authors noted that the relative contribution of these compartments to surface water was
low compared to runoff.
An important consideration resulting from these data is that any analysis of surface water
monitoring data cannot distinguish between sources of contamination. In other words,
the analysis of surface water concentrations discussed below cannot distinguish the
source of the contaminant whether it be from runoff, drift, or deposition from rainfall.
The reported value likely includes all sources of input into the surface water body, and
thus, the effect of volatilization of 2,4-D in the aquatic exposure scenarios is lessened.
44
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However, the impact of volatilization and the potential impact on off-site, non-target
terrestrial organisms in unknown and cannot be quantified.
To assess the potential for 2,4-D to partition into various media, EFED performed an
estimation of partitioning of 2,4-D acid and 2,4-D EHE with a simple fugacity model in
USEPA EpiSuite software. The fugacity model predicts that the relative percentage of
2,4-D acid that will partition into air is 0.37 percent while the relative percentage for 2,4-
D EHE is 0.48 percent. The results of the fugacity model suggest that for 2,4-D acid and
2,4-D EHE that volatilization is not predicted to be a major route of exposure.
Uncertainties associated with the use of a fugacity model are that partitioning of 2,4-D
esters to soil is estimated and that the effect of intercept and volatilization from plant
surfaces is not accounted for. These facts could result in an underestimation of the
amount partitioning to air.
It is noted that EFED's current risk assessment does account for spray drift as a process
effecting exposure through the use of PRZM/EXAMS and the drift component.
However, longer-range transport coupled with volatility and ultimately deposition via
rainfall is not accounted for in this assessment and lends additional uncertainty to the risk
assessment.
2.4.8 Mechanism of Action
2,4-D is a plant growth regulator in the phenoxy or phenoxyacetic acid family. It is most
commonly used as a post-emergence herbicide for selective control of broadleaf weeds.
2,4-D, a synthetic auxin herbicide, causes disruption of plant hormone responses.
Endogenous auxins are plant growth regulator hormones. These growth-regulating
chemicals cause disruption of multiple growth processes in susceptible plants by
affecting proteins in the plasma membrane, interfering with RNA production, and
changing the properties and integrity of the plasma membrane. Excessive cell division
and the resulting growth destroy the plant's vascular transport system. The most
susceptible tissues are those that are undergoing active cell division and growth (Gibson
and Liebman, 2002).
Plant injuries include growth and reproduction abnormalities, especially on new growth.
Broadleaf plants experience stem and petiole twisting (epinasty), leaf malformations
(parallel venation, leaf strapping, and cupping), undifferentiated cell masses and
adventitious root formation on stems, and stunted root growth. Rolled leaves (onion
leafing), fused brace roots, leaning stems, and stalk brittleness are effects observed on
grass plants. Disruption of reproductive processes may occur resulting in sterile or
multiple florets and nonviable seed production. Symptoms may appear on young growth
almost immediately after application, but death may not occur for several weeks.
2.4.9 Use Characterization
Analysis of labeled use information is the critical first step in evaluating the federal
action. The current labels for 2,4-D represent the FIFRA regulatory action; therefore,
45
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labeled use and application rates specified on the labels form the basis of this assessment.
The June 6, 2005 version of the Master Label, prepared by SRRD and supported by the
2,4-D Industry and IR-4 (Appendix N), was used for use characterization and modeling
scenario selection. The Master Label provided by SRRD does include mitigation
regarding rates and uses that resulted from the RED. EFED utilized the rates and uses as
provided in the Master Label as a detailed analysis of the current label rates was
unavailable. It is possible that not all 2,4-D labels have been updated to match the rates
and specifics on the Master Label. For those instances in which rates on the Master Label
are lower than rates on currently used labels, EFED's risk assessment may underestimate
the exposure and risk to the assessed species. In addition, SRRD has stated that the
Master Label is limited by the lack of inclusion of the following:
EPA precautionary label statements
Worker Protection Standard information other typical REIs
Complete recommendations and limitations related to efficacy, plant varieties, etc.
Ranges of rates, mixing directions, weed lists, etc. as per actual labels
Comprehensive equipment details
A very few Section 24(c) use parameters.
The assessment of use information is critical to the development of the action area and
selection of appropriate modeling scenarios and inputs.
Target pests include a wide variety of broadleaf weeds and aquatic weeds. Formulation
types registered include emulsifiable concentrate, granules, soluble concentrate/solid,
soluble concentrate/liquid, water dispersible granules (dry flowable), and wettable
powder. 2,4-D may be applied with a wide range of application equipment including
aircraft, backpack sprayer, band sprayer, boom sprayer, granule applicator, ground, hand-
held sprayer, helicopter, injection equipment, tractor-mounted granule applicator, and
tractor-mounted sprayers. Methods of application of 2,4-D may include band treatment,
basal spray treatment, broadcast, frill treatment, girdle treatment, ground spray, soil band
treatment, soil broadcast treatment, spot treatment, stump treatment, tree injection
treatment, and water-related surface treatment. 2,4-D application can be applied at
emergence, before bud break, at a dormant stage, at a dough stage, to established
plantings, foliarly, at post-emergence, at pre-emergence, at pre-harvest, and/or at pre-
plant.
The current labeled uses for 2,4-D as shown in Table 2.4 constitute the federal action
evaluated in this assessment: Soybean and cranberry are on the Master Label; however,
they are not grown in California, so they are not included in this assessment. Strawberries
are included on the Master Label, but are off-labeled for 2,4-D use in California, so they
are not included in this assessment.
46
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Tsihle 2.4 2.4-1) I ses Assessed lor ( nlilbrnin ;is derived from Muster l.sihel lor
Uereuislrsilion of 2.4-l)iehloro|)henoxvsu'elie Acid I ses developed hv SUUI)
Master Label I so (alegon
iind Delailed I sos
l abel I ses
Method1
Application Kale
(inlcnal hclwccn applicalions)
Orchard Uses
Nut Orchards, Pistachios
Acid, DMA, TIP A,
IP A, DEA, Na
G
2 apps @ 2 lb a.e./acre
(30-day interval)
Filberts
Acid, DMA, TIP A,
IP A, DEA, Na
G
4 apps @ 0.5 lb a.e./acre2
(30-day interval)
Grapes
Acid, DMA, TIP A,
IP A, DEA, Na
G
1 app @ 1.36 lb a.e./acre
Grapes (wine grapes)
Acid, DMA, TIP A,
IP A, DEA, Na
G
1 app @ 1.36 lb a.e./acre
Blueberries
Acid, DMA, TIP A,
IP A, DEA, Na
G
1 post-emergence app @ 1.4 lb a.e./acre and
1 post-harvest app 'a 1.4 lb a.e./acre
Stone and Pome Fruits
Acid, DMA, TIP A,
IP A, DEA, Na
G
2 apps @ 2 lb a.e./acre
(7 5-day interval)
Citrus
IPE
G
1 app 'a 0.1 lb a.e./acre
A
1 app 'a 0.1 lb a.e./acre
Agricultural - Food Crop Uses
Field Corn, Popcorn
Acid, DMA, TIP A,
IP A, DEA, Na, 2-
EHE, BEE
G
1 app @ 1.0 lb a.e./acre March 15,
1 app @ 0.5 lb a.e./acre April 29
1 app @ 1.5 lb a.e./acre August 15 (pre-
harvest)
A
1 app @ 1.0 lb a.e./acre March 15,
1 app @ 0.5 lb a.e./acre April 29
1 app @ 1.5 lb a.e./acre August 15 (pre-
harvest)
Sweet Corn
Acid, DMA, TIP A,
IP A, DEA, Na, 2-
EHE, BEE
G
1 app @ 1 lb a.e./acre March 15; 1 app @
0.5 lb a.e./acre April 29
A
1 app @ 1 lb a.e./acre on March 15; and 1
app (i 0.5 lb a.e./acre on April 29
Potatoes
Fresh market only
Acid, DMA, TIP A,
IP A, DEA, Na, 2-
EHE, BEE
G
2 apps @ 0.07 lb a.e./acre
(10-day interval)
A
2 apps @ 0.07 lb a.e./acre
(10-day interval)
Sugarcane4
Acid, DMA, TIP A,
IP A, DEA, Na
G
1 pre-emergence and 1 post-emergence app
(i 2 lb a.e./acre (20-day interval)
A
1 pre-emergence and 1 post-emergence app
'a, 2 lb a.e./acre (20-day interval)
Cereal Grains
Wheat, Barley, Millet, Oats,
Rye
Acid, DMA, TIP A,
IP A, DEA, Na, 2-
EHE, BEE
G
1 post-emergence app @ 1.25 lb a.e./acre
and 1 pre-harvest app @ 0.5 lb a.e./acre
(90-day interval)
A
1 post-emergence app @ 1.25 lb a.e./acre
and 1 pre-harvest app @ 0.5 lb a.e./acre
(90-day interval)
Grain or Forage Sorghum
Acid, DMA, TIP A,
IP A, DEA, Na
G
1 post-emergence app @ 1.0 lb a.e./acre
A
1 post-emergence app @ 1.0 lb a.e./acre
2-EHE, BEE
G
1 post-emergence app @ 0.5 lb a.e./acre
47
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Tsihle 2.4 2.4-1) I ses Assessed lor ( nlilbrnin ;is derived from Muster l.sihel lor
Ueregistrsilion ol' 2.4-l)ichl»r»j)heii»\v;u'elic Acid I ses developed hv SUUI)
Msisler l.sihel I se( silegnn
sind Detailed I sos
l abel I ses
Method'
Application Kale
(inlcnsil between sipplicsitions)
A
1 pobl-eniergence app a U.5 lb a.e.. acre
Hops
Acid, DMA, TIP A,
IP A, DEA, Na
G
3 apps @ 0.5 lb a.e./acre
(30-day interval)
A
3 apps @ 0.5 lb a.e./acre
(30-day interval)
Asparagus
Acid, DMA, TIP A,
IP A, DEA, Na
G
2 apps @ 2 lb a.e./acre
(30-day interval)
A
2 apps @ 2 lb a.e./acre
(30-day interval)
Fallowland and Crop
Stubble
Acid, DMA, TIP A,
IP A, DEA, Na, 2-
EHE, BEE
G
2 apps @ 2 lb a.e./acre
(30-day interval)
A
2 apps @ 2 lb a.e./acre
(30-day interval)
Agricultural - Non-food Crop Uses
Established Grass Pastures,
Rangeland, Perennial
Grassland Not in
Agricultural Production
Acid, DMA, TIP A,
IP A, DEA, Na, 2-
EHE, BEE
G
2 apps @ 2 lb a.e./acre
(30-day interval)
Non-agricultural Uses
Non-cropland
Fencerows, Hedgerows,
Roadsides, Ditches, Rights-
of-way, Utility power lines,
Railroads, Airports,
Industrial sites, and Other
non-crop areas
Acid, DMA, TIP A,
IP A, DEA, Na, 2-
EHE, BEE
G
1 app 'a 4 lb a.e./acre
A
1 app @ 4 lb a.e./acre
Forestry
Forest site preparation, Forest
roadsides, Brush control,
Established conifer release
including Christmas trees and
reforestation areas
Acid, DMA, TIP A,
IP A, DEA, Na, 2-
EHE, BEE
G
1 app (a) 4 lb a.e./acre
A
1 app @ 4 lb a.e./acre
Tree and Brush Control
Alder, Ash, Aspen, Birch,
Blackgum, Cherry, Elm, Oak,
Sweetgum, Tulip poplar,
Willow, and Others
Acid, DMA, TIP A,
IP A, DEA, Na, 2-
EHE, BEE
G
1 app (i 4 lb a.e./acre
A
1 app @ 4 lb a.e./acre
Ornamental Turf
Golf courses, Cemeteries,
Parks, Sports fields,
Turfgrass, Lawns and other
grass areas
Acid, DMA, TIP A,
IP A, DEA, Na, 2-
EHE, BEE
G
2 apps @ 1.5 lb a.e./acre
(21-day interval)
A
2 apps @ 1.5 lb a.e./acre
(21-day interval)
Grass Grown for Seed and
Sod
Acid, DMA, TIP A,
IP A, DEA, Na, 2-
EHE, BEE
G
2 apps @ 2 lb a.e./acre
(21-day interval)
A
2 apps @ 2 lb a.e./acre
(21-day interval)
Direct Application to Water Uses
Rice
Acid, DMA, TIP A,
G & A
1 app (i 1.5 lb a.e./acre
48
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Tsihle 2.4 2.4-1) I ses Assessed lor ( nlilbrnin ;is derived from Muster l.sihel lor
Ueregistrsilion of 2.4-l)ichl»r»j)heii»\v;u'elic Acid I ses developed hv SUUI)
Msisler l.sihel I so ( silesion
sind Detailed I sos
l.sihel I ses
Mollind'
Application Kale
(inlcnsil hclwccn sipplicsilions)
IP A, DEA, Na
Aquatic Weed Control
Surface application or
subsurface injection for
submersed weeds
Acid, DMA, TIP A,
IP A, DEA, Na, BEE
G & A
1 app @ 10.8 lb a.e./acre foot
Aquatic Weed Control
Irrigation ditchbank
application
Acid, DMA, TIP A,
IP A, DEA, Na, BEE
G & A
2 app @ 2.0 lb a.e./acre
(30-day interval)
Aquatic Weed Control
Surface application for
floating and emergent aquatic
weeds
Acid, DMA, TIP A,
IP A, DEA, Na, BEE
G & A
2 app @ 4.0 lb a.e./acre
(21-day interval)
1 G = ground application. A = aerial application.
2 The Master Label indicates a maximum single application rate of 1.0 lb a.e./lOO gallons spray for filberts,
SRRD verified that this rate is equivalent to a maximum single application rate should of 0.5 lb a.e./acre, which
represents a conservative estimate.
A national map (Figure 2.3) showing the estimated poundage of 2,4-D agricultural uses
across the United States is provided below. The map was downloaded from a U.S.
Geological Survey (USGS), National Water Quality Assessment Program (NAWQA)
website (http://water.usgs.gov/nawqa/pnsp/usage/maps/). All registered uses and
applications are not necessarily included in this figure (e.g., direct water application).
49
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2,4-D - herbicide
2002 estimated annual agricultural use
Crops
Total
Percent
pounds applied
national use
pastureland
21947880
55.18
wheat for grain
5443483
13.69
other hay
2820947
7.09
corn
2496503
6.28
cropland in summer fallow
1550082
3.90
soybeans
1504323
3.78
sugarcane
1426739
3.59
barley for grain
561492
1.41
sorghum
554666
1.39
rice
525714
1.32
Average annual use of
active ingredient
(pounds per square mile of agricultural
land in county)
~ no estimated use
~ 0.001 to 1.084
~ 1.085 to 3.241
~ 3.242 to 7.026
~ 7.027 to 13.158
¦ >=13.159
Figure 2.3 2,4-D Use in Total Pounds per County. This map does not necessarily
include all registered uses, e.g., direct water application.
According to 2002 annual agricultural use estimates, the total 2,4-D use was about 39.8
million pounds. Among them, pastureland use was the dominant one (55.18%). The other
major uses were as follows: wheat for grain (13.69%), other hay (7.09%), corn (6.28%),
cropland in summer fallow (3.90%), soybean (3.78%), sugarcane (3.59%), barley for
grain (1.41%), sorghum (1.39%) and rice (1.32%).
The Agency's Biological and Economic Analysis Division (BEAD) provides an analysis
of both national- and county-level usage information (Kaul and Jones, 2006) using state-
level usage data obtained from USDA-NASS2, Doane (www.doane.com; the full dataset
is not provided due to its proprietary nature) and the California's Department of Pesticide
Regulation Pesticide Use Reporting (CDPR PUR) database3.
2 United States Depart of Agriculture (USDA). National Agricultural Statistics Service (NASS) Chemical
Use Reports provide summary pesticide usage statistics for select agricultural use sites by chemical, crop
and state. See http://www.usda.eov/nass/pubs/estindx 1 ,htm#agchem.
3 The California Department of Pesticide Regulation's Pesticide Use Reporting database provides a census
of pesticide applications in the state. See http://www.cdpr.ca.gov/docs/pur/pumiain.htm.
50
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CDPR PUR is considered a more comprehensive source of usage data than USDA-NASS
or EPA proprietary databases, and thus, the usage data reported for 2,4-D by county in
this California-specific assessment were generated using CDPR PUR data. Eight years
(1999-2006) of usage data were included in this analysis. Data from CDPR PUR were
obtained for every reported pesticide application made on every use site at the section
level (approximately one square mile) of the public land survey system. BEAD
summarized these data to the county-level by site, pesticide, and unit area treated.
Calculating county-level usage involved summarizing across all applications made within
a section and then across all sections within a county for each use site and for each
pesticide. The county-level usage data that were calculated include average annual
pounds applied, average annual area treated, and average and maximum application rate
across all eight years.
From 1999 to 2006, 2,4-D was used on 97 crops or sites in 58 counties in California. For
all technical forms (e.g., acid, DMA, TIP A), PUR data were reported in lb a.i./acre.
Usage values reported in this assessment were also reported as lb a.i./acre. The PUR
database reported usage data individually for each of the technical forms; no usage data
were recorded for 2,4-D sodium salt and 2,4-D IPA. Reported usage data is a summation
of usage data for each form on the basis of lb a.i./acre; no conversion to lb a.e./acre was
performed. Usage data is summarized for each crop category on the Master Label (Table
2.5) and for each county (Table 2.6). Data for each individual PUR use category is
provided in Appendix C.
The herbicide was used in the greatest quantity on wheat with an average yearly
application of-106,200 lb a.i./year. Almond, right-of-ways, uncultivated, landscape
maintenance and oat followed with -70,400 lb a.i./year, -37,700 lb a.i./year, -24,500 lb
a.i./year, -22,700 lb a.i./year, and -21,100 lb a.i./year, respectively. The highest average
application rate for any single use over the eight year period was 5.71 lb a.i./acre applied
to regular pest control. The greatest quantity of 2,4-D was applied in San Joaquin County
with a yearly average application of-40,400 lb a.i./year followed by Merced, Kings,
Imperial and Solano counties with -33,700 lb a.i./year, -33,100 lb a.i./year, -33,0700 lb
a.i./year, and -28,300 lb a.i./year, respectively. The highest average county application
rate over the eight year period was 2.83 lb a.i./acre applied in Alpine County; however,
only 2.83 lb was applied in total in this county.
Almost of all the highest single application rates recorded in the 1999 to 2006 CDPR
PUR data greatly exceed the maximum application rates permitted on 2,4-D labels and
likely indicate data entry errors in the pounds applied or the acres treated data fields. The
95th and 99th percentile estimations of application rates aggregated by cropping category
were, for the majority, less than the maximum labeled rates.
Typically, the average application rate (based on many records from the data set) is far
below the maximum label-permitted application rate. For instance, the average
application rate for wheat (0.73 lb a.i./acre) was only 58.4 % of the maximum labeled
rate (1.25 lb a.i./acre). Although not often used and applied to small areas, there were a
few instances where the average annual application rate for a crop use exceeded the
51
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maximum labeled rate. For example, the average application rate for Christmas tree
(4.24 lb a.i./acre) was 6% greater than the maximum labeled rate (4.0 lb a.i./acre);
however, only about 4.24 lb a.i./year was applied at this rate. There are a few limitations
to the CDPR PUR data. There were several uses reported in the PUR data that were either
not registered or were misuses according to labels; these accounted for approximately
5,400 lb a.i./year.
For almost all of the reported crops and uses in the CDPR PUR data, the 95th and 99th
percentile estimations of application rates are also well below the maximum labeled rates.
Again, the few exceptions to this likely occurred due to a few applications made to small
areas. Only the maximum label application rates were modeled for this assessment.
Evaluation of the usage data (aggregated general cropping category) showed that 2,4-D
was applied in the greatest quantity to cereal grains with an average annual application of
-150,600 lb a.i./year. The nuts, right of ways, pasture/grassland, pome/stone fruits, and
turf cropping categories followed with -85,900 lb a.i./year, -60,400 lb a.i./year, -43,900
lb a.i./year, -24,500 lb a.i./year, and -19,300 lb a.i./year, respectively.
A summary of all 2,4-D uses based on general cropping categories in California is
provided in Table 2.5, and county use data is provided in Table 2.6. More detailed
cropping use and acreage information based on specific PUR crop categories is available
in Appendix C.
Table 2.5 Summary of California Department of Pesticide Registration (CI)PU)
Pesticide I se Reporting (PI U) 2.4-1) I se Data from 1999 to 2006
A\er;ige Aiimi;il
\pplic;ilion K;iu> (II) ;i.i./;iciv)
(iciHTiil Cropping Csilcgon
Application (II)
;i.i./u-:ir)
\\(;
«)5lh " iiilo
<)<) V iiilo
MAX
Cereal Grains,
Grain or Forage Sorghum
150,631
0.84
1.34
1.61
61.87
Nut Orchards, Pistachios,
Filberts
85,903
0.60
0.91
1.20
27.03
Right of way, landscape
maintenance
60,362
1.66
2.60
3.40
82.08
Grass Pastures, rangeland
43,924
1.10
2.09
2.70
29.41
Pome Fruits, Stone Fruits
24,524
0.489
0.75
0.93
15.50
Grass Pastures, rangeland, grass
Grown for Seed and Sod,
19,322
0.95
1.28
1.45
44.78
Ornamental Turf
Field Corn, Popcorn, Sweet
Corn, Sunflower
13,677
0.64
0.94
1.03
10.26
Grapes
13,520
0.65
1.38
1.61
10.04
Citrus
13,155
0.28
0.40
0.44
22.00
Forestry, Tree and Brush
Control, Christmas trees
7,987
3.00
4.35
4.88
42.41
Rice
7,827
0.45
0.76
1.13
5.43
Structural pest control, industrial
sites
937
1.20
1.74
1.74
2.40
52
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Tsihle 2.5 Siiniiiiiirv ol'C :ilil'orni;i Depnrt menl of Pesticide Registration (CDPU)
Pesticide I se Reporting (PI U) 2.4-1) I se I'rom 1999 to 2006
A\cr;iiic Aiimi;il
\ppliciilion Kiiic ill) ii.i./iiciv)
(>cncr;il ( mppinti ( iileiion
Application (II)
;i.i./>c;ir)
\\(;
95(h " iiile
')') " nik-
MAX
Water area
374
3.62
3.77
4.46
13.80
Asparagus, dried bean, fruiting
pepper, fallow land
310
0.63
0.70
0.70
1.72
Potato
42
0.64
0.79
0.79
1.13
Sugar beet, sugar cane
37
1.02
1.17
1.17
1.72
Reported PUR data, uses not
represented on Master Label
9870
1.12
3.10
4.91
19.70
Uses Without PRZM Modeling
Scenarios
30,153
1.78
2.49
2.50
61.08
TOTAL
482,560
Tsihle 2.6 Siiiiiiiisii'y orCsililorniii Dcpnrlmcnl of Pesticide Uegislrsilion (CDPU)
Pesticide I ssige Reporting (PI U) l);it;i IVoni 1999 to 2006 lor Comities
A\cr;iiic Aniuiiil
Appliciilion K;ilc(ll> ii.i./iicrc)
( niin(\
Application
(II) ;i.i.Aciir)
A\cr;iiic
')5lh V-iiilc
')') V-iiilc
Miixiiiiiini
SAN JOAQUIN
40,352
0.803
1.151
1.682
61.866
MERCED
33,696
0.776
1.178
1.378
9.010
KINGS
33,097
0.778
1.115
1.150
9.475
IMPERIAL
32,975
1.030
1.378
1.392
8.079
SOLANO
28,329
0.806
1.225
2.115
16.352
FRESNO
28,092
0.654
1.159
1.304
10.037
YOLO
26,369
0.896
1.138
1.940
27.029
STANISLAUS
23,870
0.910
1.319
1.545
14.250
TULARE
23,598
0.566
0.925
1.590
22.000
GLENN
19,361
0.692
1.070
1.373
15.754
BUTTE
18,9645
0.759
1.141
1.291
8.478
SACRAMENTO
16,657
1.228
1.472
1.785
13.800
MADERA
14,745
0.800
1.261
1.394
16.369
SISKIYOU
13,378
1.249
3.023
3.162
44.780
SUTTER
11,605
0.627
0.954
1.150
5.626
RIVERSIDE
11,164
1.571
2.760
3.066
82.075
MODOC
9,244
0.834
1.290
1.335
10.278
KERN
9,162
1.293
2.882
2.986
61.077
SAN LUIS OBISPO
8,983
0.567
0.864
1.703
22.611
COLUSA
8,214
0.545
0.853
0.987
5.626
ALAMEDA
7,197
1.477
3.731
5.308
31.655
CONTRA COSTA
6,445
1.223
2.071
2.176
9.002
TEHAMA
6,146
0.788
1.229
1.469
15.504
MONTEREY
5,061
0.860
1.228
1.492
4.524
LOS ANGELES
5,029
1.854
3.384
3.480
19.000
53
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Table 2.6 Summary nt'CaliCoi'iiia Department of Pesticide Registration (CI)PK)
Pesticide I sage Reporting (PI U) Data from 1999 to 2006 lor C ounties
SHASTA
4,031
1.033
1.374
1.886
7.727
SAN BERNARDINO
3,107
0.967
1.155
1.266
4.341
SANTA BARBARA
3,000
0.833
1.240
3.080
26.257
SAN BENITO
2,830
0.917
1.344
1.397
7.648
ORANGE
2,817
1.413
2.313
2.313
13.480
VENTURA
2,726
0.960
1.554
2.969
40.718
LASSEN
2,689
1.076
1.730
2.136
17.364
SANTA CLARA
2,340
0.834
1.388
1.914
9.892
SONOMA
2,074
0.988
1.430
1.602
9.501
YUBA
1,762
0.700
1.088
1.182
3.291
SAN DIEGO
1,755
0.564
1.109
1.168
13.346
PLACER
1,288
1.030
1.899
1.975
13.573
DEL NORTE
1,124
0.977
0.996
0.996
11.354
SAN MATEO
1,084
2.282
4.040
8.112
29.407
LAKE
951
1.087
1.524
3.027
16.879
AMADOR
937
0.931
1.232
1.358
5.652
MARIN
858
1.483
2.131
2.211
6.773
HUMBOLDT
792
0.818
1.465
1.712
6.362
TUOLUMNE
653
0.701
1.558
1.692
6.873
CALAVERAS
553
1.226
2.957
3.815
13.567
SIERRA
541
1.111
1.418
1.465
5.652
MENDOCINO
525
1.619
5.315
5.316
42.413
PLUMAS
522
0.994
1.329
1.406
3.815
NEVADA
324
1.162
2.143
2.143
5.805
EL DORADO
281
1.406
2.150
2.150
6.783
INYO
273
1.786
2.964
2.964
4.505
NAPA
263
0.586
0.924
0.924
1.697
MONO
255
1.968
2.005
2.005
4.076
TRINITY
244
1.771
5.829
6.318
13.188
SAN FRANCISCO
117
NR
NR
NR
NR
MARIPOSA
70
0.979
1.464
1.592
2.287
SANTA CRUZ
31
0.702
0.751
0.986
2.110
ALPINE
3
2.828
2.828
2.828
2.828
TOTAL
482,560
NR - Not Reported
2.5 Assessed Species
Table 2.7 provides a summary of the current distribution, habitat requirements, and life
history parameters for the two listed species being assessed. More detailed life history
and distribution information can be found in Attachments 1 and 3. See Figures 2.4.a
and 2.4.b for maps of the current range and designated critical habitat of the assessed
listed species.
54
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Table 2.7. Summary of Current Distribution, Habitat Ret
uirements, and Life History Information for the Assessed Listed Species'
Assessed Species
Size
Current Range
Habitat Ty pe
Designated
Critieal
Habitat?
Reproductive
Cycle
Diet
California red-
legged frog
(Rana aurora
draytonii)
Adult
(85-138 cm
in length),
Females -
9-238 g,
Males -
13-163 g;
Juveniles
(40-84 cm
in length)
Northern CA coast, northern
Transverse Ranges, foothills of
Sierra Nevada, and in southern CA
south of Santa Barbara
Freshwater perennial
or near-perennial
aquatic habitat with
dense vegetation;
artificial
impoundments;
riparian and upland
areas
Yes
Breedins: Nov. to Aor.
Tadoolcs: Dec. to Mar.
Youns iuveniles: Mar. to
Sept.
Aciuatic-Dhasc2: aleae.
freshwater aquatic
invertebrates
Terrestrial-ohase:
aquatic and terrestrial
invertebrates, small
mammals, fish and
frogs
AW
(Masticophis
lateralis
euryxanthus)
3-5ft
Contra Costa and Alameda
Counties in California (additional
occurrences in San Joaquin and
Santa Clara Counties)
Primarily, scrub and
chaparral
communities. Also
found in grassland,
oak savanna, oak-bay
woodland, and
riparian areas.
Yes
Emerge from hibernation
and begin mating from
late March through mid-
June. Females lay eggs in
May through July. Eggs
hatch from August
through November.
Hibernate during the
winter months.
Lizards, small
mammals, nesting
birds, other snakes
including rattlesnakes
1 For more detailed information on the distribution, habitat requirements, and life history information of the assessed listed species, see Attachments 1 and 3
2For the purposes of this assessment, tadpoles and submerged adult frogs are considered "aquatic" because exposure pathways in the water are considerably different
than those that occur on land.
3Oviparous = eggs hatch within the female's body and young are born live.
55
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Legend
] Recovery Unit Boundaries
Currently Occupied Core Areas
| Critical Habitat
| CNDDB Occurence Sections
County Boundaries q 45
I 1 i_
180 Miles
Figure 2.4.a Recovery Unit, Core Area, Critical Habitat, and Occurrence
Designations for CRLF
Recovery Units
Sierra Nevada Foothills and Central Valley
North Coast Range Foothills and Western
Sacramento River Valley
North Coast and North San Francisco Bay
South and East San Francisco Bay
Central Coast
Diablo Range and Salinas Valley
Northern Transverse Ranges and Tehachapi
Mountains
Southern Transverse and Peninsular Ranges
Core Areas
1.
Feather River
2.
Yuba River- S. Fork-Feather River
3.
Traverse Creek/ Middle Fork/ American R. Rubicon
4.
Cosumnes River
5.
South Fork Calaveras River*
6.
Tuolumne River*
7.
Piney Creek*
8.
Cottonwood Creek
9.
Putah Creek - Cache Creek*
10.
Lake Berryessa Tributaries
11.
Upper Sonoma Creek
12.
Petaluma Creek - Sonoma Creek
13.
Pt. Reyes Peninsula
14.
Belvedere Lagoon
15.
Jameson Canyon Lower Napa River
16.
East San Francisco Bay
17.
Santa Clara Valley
18.
South San Francisco Bay
19.
Watsonville Slough-Elkhorn Slough
20.
Carmel River Santa Lucia
21.
Gablan Range
22.
Estexo Bay
23.
Arroyo Grange River
24.
Santa Maria River Santa Ynez River
25.
Sisquoc River
26.
Ventura River Santa Clara River
27.
Santa Monica Bay Venura Coastal Streams
28.
Estrella River
29.
San Gabriel Mountain*
30.
Forks of the Mojave*
31.
Santa Ana Mountain*
32.
Santa Rosa Plateau
33.
San Luis Ray*
34.
Sweetwater*
35.
Laguna Mountain*
* Core areas that were historically occupied by the California
red-legged frog are not included in the map.
56
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San Francisco
Map created by US EPA on 10/07/D8. Projection: Albers Equal Area
Conic USGS, North American Datum of 1983 (NAD 1983). California
county boundaries, source: ESRI 2002. Species data source: see text.
1:500,000
Alameda whipsnake habitat areas
Sonoma Napa
Marin
Alameda
Joaquin
Solano
Sacramento
San Mateo
0 2.5 5 10 Miles
Alameda whipsnake occurrence sections
Alameda whipsnake critical habitat
CA counties
Santa Clara
Stanislaus
Figure 2.4.b Critical Habitat and Occurrence Designations for AW
57
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2.6 Designated Critical Habitat
Critical habitats have been designated for the CRLF and AW.
'Critical habitat' is defined in the ESA as the geographic area occupied by the species at
the time of the listing where the physical and biological features necessary for the
conservation of the species exist, and there is a need for special management to protect
the listed species. It may also include areas outside the occupied area at the time of
listing if such areas are 'essential to the conservation of the species.' Critical habitat
receives protection under Section 7 of the ESA through prohibition against destruction or
adverse modification with regard to actions carried out, funded, or authorized by a federal
agency. Section 7 requires consultation on federal actions that are likely to result in the
destruction or adverse modification of critical habitat.
To be included in a critical habitat designation, the habitat must be 'essential to the
conservation of the species.' Critical habitat designations identify, to the extent known
using the best scientific and commercial data available, habitat areas that provide
essential life cycle needs of the species, or areas that contain certain primary constituent
elements (PCEs) (as defined in 50 CFR 414.12(b)). PCEs include, but are not limited to,
space for individual and population growth and for normal behavior; food, water, air,
light, minerals, or other nutritional or physiological requirements; cover or shelter; sites
for breeding, reproduction, rearing (or development) of offspring; and habitats that are
protected from disturbance or are representative of the historic geographical and
ecological distributions of a species. Table 2.8 describes the PCEs for the critical
habitats designated for the CRLF and AW.
Table 2.8 Designated Critical Habitat PC lis lor the ( KM and AW 1
Species
P( I s
Reference
CRLF
Alteration of channel/pond morphology or geometry and/or increase
in sediment deposition within the stream channel or pond.
50 CFR 414.12(b),
2006
Alteration in water chemistry/quality including temperature,
turbidity, and oxygen content necessary for normal growth and
viability of juvenile and adult CRLFs and their food source.
Alteration of other chemical characteristics necessary for normal
growth and viability of CRLFs and their food source.
Reduction and/or modification of aquatic-based food sources for pre-
metamorphs (e.g., algae)
Elimination and/or disturbance of upland habitat; ability of habitat to
support food source of CRLFs: Upland areas within 200 ft of the
edge of the riparian vegetation or dripline surrounding aquatic and
riparian habitat that are comprised of grasslands, woodlands, and/or
wetland/riparian plant species that provides the CRLF shelter,
forage, and predator avoidance
Elimination and/or disturbance of dispersal habitat: Upland or
riparian dispersal habitat within designated units and between
occupied locations within 0.7 mi of each other that allow for
movement between sites including both natural and altered sites
which do not contain barriers to dispersal
58
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Table 2.8 Designated ( ritical 1 lahilal P(T.s lor the ( UI.I- and AW 1
Species
P( I s
Reference'
Reduction and/or modification of food sources for terrestrial phase
juveniles and adults
Alteration of chemical characteristics necessary for normal growth
and viability of juvenile and adult CRLFs and their food source.
AW
Scrub/shrub communities with a mosaic of open and closed canopy
71 FR 58175 58231,
2006
Woodland or annual grassland plant communities contiguous to
lands containing scrub/shrub communities with a mosaic of open and
closed canopy
Lands containing rock outcrops, talus, and small mammal burrows
within or adjacent to 1) scrub/shrub communities with a mosaic of
open and closed canopy and/or 2) woodland or annual grassland
plant communities contiguous to lands containing scrub/shrub
communities with a mosaic of open and closed canopy
1 These PCEs are in addition to more general requirements for habitat areas that provide essential life cycle needs
of the species such as, space for individual and population growth and for normal behavior; food, water, air, light,
minerals, or other nutritional or physiological requirements; cover or shelter; sites for breeding, reproduction,
rearing (or development) of offspring; and habitats that are protected from disturbance or are representative of the
historic geographical and ecological distributions of a species.
More detail on the designated critical habitat applicable to this assessment can be found
in Attachment 1 (CRLF) and Attachment 3 (AW). Activities that may destroy or
adversely modify critical habitat are those that alter the PCEs and jeopardize the
continued existence of the species. Evaluation of actions related to use of 2,4-D that may
alter the PCEs of the designated critical habitats for the CRLF and AW form the basis of
the critical habitat impact analysis.
As previously noted in Section 2.1, the Agency believes that the analysis of direct and
indirect effects to listed species provides the basis for an analysis of potential effects on
the designated critical habitats. Because 2,4-D is expected to directly impact living
organisms within the action area, critical habitat analysis for 2,4-D is limited in a
practical sense to those PCEs of critical habitats that are biological or that can be
reasonably linked to biologically mediated processes.
2.7 Action Area
For listed species assessment purposes, the action area is considered to be the area
affected directly or indirectly by the federal action and not merely the immediate area
involved in the action (50 CFR 402.02). It is recognized that the overall action area for
the national registration of 2,4-D is likely to encompass considerable portions of the
United States based on the large array of agricultural and/or non-agricultural uses.
However, the scope of this assessment limits consideration of the overall action area to
those portions that may be applicable to the protection of the CRLF and AW and their
designated critical habitats within the state of California. Although the watershed for the
San Francisco Bay extends northward into the very southwestern portion of Lake County,
Oregon, and westward into the western edge of Washoe County, Nevada, the non-
California portions of the watershed are small and very rural with little, if any,
59
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agriculture. Therefore, no use of 2,4-D is expected in these areas, and they are not
considered as part of the action area applicable to this assessment.
The definition of action area requires a stepwise approach that begins with an
understanding of the federal action. The federal action is defined by the currently labeled
uses for 2,4-D. An analysis of labeled uses and review of available product labels was
completed. This analysis was based on the Master Label (Appendix N) as supported by
the 2,4-D Industry and the Interregional Research Project Number 4 (IR-4). Several of
the currently labeled uses are special local needs (SLN) uses or are restricted to specific
states other than California and are excluded from this assessment. In addition, a
distinction has been made between food use crops and those that are non-food/non-
agricultural uses. Uses relevant to the assessed species ans which constitute the federal
action are listed in Table 2.4.
Following a determination of the assessed uses, the potential "footprint" of 2,4-D use
patterns (i.e., the area where pesticide application occurs) is determined. This "footprint"
represents the initial area of concern, based on an analysis of available land cover data for
the state of California. Deriving the geographical extent of this portion of the action area
is based on consideration of the types of effects that 2,4-D may be expected to have on
the environment, the exposure levels to 2,4-D that are associated with those effects, and
the best available information concerning the use of 2,4-D and its fate and transport
within the state of California. Specific measures of ecological effect for the CRLF and
AW that define the action area include any direct and indirect toxic effect to the CRLF
and AW and any potential modification of its critical habitat, including reduction in
survival, growth, and fecundity as well as the full suite of 2,4-D effects available in the
effects literature. Therefore, the action area extends to a point where environmental
exposures are below any measured lethal or 2,4-D effect threshold for any biological
entity at the whole organism, organ, tissue, and cellular level of organization. In
situations where it is not possible to determine the threshold for an observed effect, the
action area is not spatially limited and is assumed to be the entire state of California.
Based on the broad range of 2,4-D use patterns, the large geographic coverage of those
uses, as well as the large total poundage used, the entire state of California is considered
to be the initial area of concern for this assessment.
Once the initial area of concern is defined, the next step is to define the potential
boundaries of the action area by determining the extent of offsite transport via spray drift
and runoff where exposure of one or more taxonomic groups to the pesticide exceeds the
listed species LOCs.
The Agency's approach to defining the action area under the provisions of the Overview
Document (U.S. EPA, 2004) considers the results of the risk assessment process to
establish boundaries for that action area with the understanding that exposures below the
Agency's defined Levels of Concern (LOCs) constitute a no-effect threshold. Deriving
the geographical extent of this portion of the action area is based on consideration of the
types of effects that 2,4-D may be expected to have on the environment, the exposure
levels to 2,4-D that are associated with those effects, and the best available information
60
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concerning the use of 2,4-D and its fate and transport within the state of California.
Specific measures of ecological effect for the assessed species that define the action area
include any direct and indirect toxic effect to the assessed species and any potential
modification of its critical habitat, including reduction in survival, growth, and fecundity
as well as the full suite of sublethal effects available in the effects literature. Therefore,
the action area extends to a point where environmental exposures are below any
measured lethal or sublethal effect threshold for any biological entity at the whole
organism, organ, tissue, and cellular level of organization. In situations where it is not
possible to determine the threshold for an observed effect, the action area is not spatially
limited and is assumed to be the entire state of California.
Due to the lack of a defined no effect concentration in a guideline terrestrial plant study
(vegetative vigor, tomato and turnip NOAEC < 0.00134 lb a.e./acre for dry weight,
MRID 471060-04), the spatial extent of the action area (i.e., the boundary where
exposures and potential effects are less than the Agency's LOC) for 2,4-D cannot be
determined. Therefore, it is assumed that the action area encompasses the entire state of
California, regardless of the spatial extent (i.e., initial area of concern or footprint) of the
pesticide use(s).
2.8 Assessment Endpoints and Measures of Ecological Effect
Assessment endpoints are defined as "explicit expressions of the actual environmental
value that is to be protected."4 Selection of the assessment endpoints is based on valued
entities (e.g., CRLF and AW), organisms that are important in the life cycle of the
assessed species, and the PCEs of its designated critical habitat), the ecosystems
potentially at risk (e.g., water bodies, riparian vegetation, and upland and dispersal
habitats), the migration pathways of 2,4-D (e.g., runoff, spray drift, etc.), and the routes
by which ecological receptors are exposed to 2,4-D (e.g., direct contact, etc.).
2.8.1 Bridging Strategy for Toxicological Data
EFED established a strategy for ecological toxicity studies submitted in support of 2,4-D
and its formulations. In this document, the term formulation is used to refer to the 2,4-D
Task Force supported technical formulations listed below, while the term end use product
is used to refer to any formulated product including mixtures of pesticide sold in the US.
All toxicity values have been converted to the acid equivalent (a.e.) based on the ratio of
molecular weights.
For aquatic animals (including aquatic phase amphibians) and plants, data evaluating 2,4-
D acid and salts have been bridged, while the data evaluating the three esters was
separately bridged. On an a.e. basis, toxicity to the acid and salts is comparable; however,
toxicity to the esters tends to be two to three orders of magnitude higher. In addition, fate
data were submitted suggesting that the salts dissociate rapidly to the acid, on the order of
several minutes. However the esters may take longer to hydrolyze to the acid, especially
depending on pH of the water. For terrestrial animals (including terrestrial phase
4FromU.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
61
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amphibians) and plants, data evaluating 2,4-D acid, salts and esters have been bridged.
Within an organism group, the variation in the toxicity endpoints is less than two orders
of magnitude, and for some groups, the variation is less than one order of magnitude.
Within each of these bridged groups of 2,4-D formulations, the most sensitive toxicity
endpoint was used for risk estimation. Toxicity data were not available for all taxa and all
formulations. In those cases it was assumed that toxicity would be similar as in the other
formulations in the same group. Table 2.9 summarizes 2,4-D bridging strategies for
estimating acute and chronic toxicity to aquatic and terrestrial organisms and plants.
Table 2.9 Summary of toxicity bridging strategies lor 2.4-1)
. \ciil and Salts bridged f or estimating acute toxicity to aquatic organisms
and plants '
l»C'Code
Chomicid Name
030001
2,4D acid
030004
2,4D sodium salt
030016
2,4D diethanolamine (DEA) salt
030019
2,4D dimethylamine (DMA) salt
030025
2,4D Isoproylamine (IPA) salt
030035
2,4D triisopropanolamine (TIPA) salt
listers bridged for estimating acute toxicity to aquatic organisms
and plants
l»C Code
Chemical Nitme
030053
2,4D butoxyethyl (BEE) ester
030063
2,4D 2 ethylhexyl ester (EHE)
030066
2,4D isopropyl ester (IPE)
. \cid. Salts, and listers bridged for estimating acute and chronic toxicity
to terrestrial organisms and plants
PC Code
Chemical Nnmo
030001
:,4D acid
030004
2,4D sodium salt
030016
2,4D diethanolamine (DEA) salt
030019
2,4D dimethylamine (DMA) salt
030025
2,4D Isoproylamine (IPA) salt
030035
2,4D triisopropanolamine (TIPA) salt
030053
2,4D butoxyethyl (BEE) ester
030063
2,4D 2 ethylhexyl ester (EHE)
030066
2,4D isopropyl ester (IPE)
aFor aquatic organisms, chronic toxicity data from acid and salts also used for
chronic toxicity to esters, as long-term exposure to the esters was not expected.
2.8.2 Assessment Endpoints
Assessment endpoints for the CRLF and AW include direct toxic effects on the survival,
reproduction, and growth of individuals, as well as indirect effects, such as reduction of
the prey base or modification of their habitats. In addition, potential modification of
critical habitat is assessed by evaluating potential effects to PCEs, which are components
of the habitat areas that provide essential life cycle needs of the assessed species. Each
62
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assessment endpoint requires one or more "measures of ecological effect," defined as
changes in the attributes of an assessment endpoint or changes in a surrogate entity or
attribute in response to exposure to a pesticide. Specific measures of ecological effect are
generally evaluated based on acute and chronic toxicity information from registrant-
submitted guideline tests that are performed on a limited number of organisms.
Additional ecological effects data from the open literature are also considered. It should
be noted that assessment endpoints are limited to direct and indirect effects associated
with survival, growth, and fecundity, and do not include the full suite of sublethal effects
used to define the action area. According to the Overview Document (U.S. EPA, 2004),
the Agency relies on acute and chronic effects endpoints that are either direct measures of
impairment of survival, growth, or fecundity or endpoints for which there is a
scientifically robust, peer-reviewed relationship that can quantify the impact of the
measured effect endpoint on the assessment endpoints of survival, growth, and fecundity.
A discussion of all the toxicity data available for this risk assessment, including resulting
measures of ecological effect selected for each taxonomic group of concern, is included
in Section 4 of this document. A summary of the assessment endpoints and measures of
ecological effect selected to characterize potential assessed direct and indirect risks for
each of the assessed species associated with exposure to 2,4-D is provided in Section 2.5
and Table 2.10.
As described in the Agency's Overview Document (U.S. EPA, 2004), the most sensitive
endpoint for each taxon is used for risk estimation. For this assessment, evaluated taxa
include aquatic-phase amphibians, freshwater fish, freshwater invertebrates, aquatic
plants, birds (surrogate for terrestrial-phase amphibians), mammals, terrestrial
invertebrates, and terrestrial plants. Acute (short-term) and chronic (long-term) toxicity
information is characterized based on registrant-submitted studies and a comprehensive
review of the open literature on 2,4-D.
Table 2.10 identifies the taxa used to assess the potential for direct and indirect effects
from the uses of 2,4-D for each listed species assessed here. The specific assessment
endpoints used to assess the potential for direct and indirect effects to each listed species
are provided in Table 2.11.
63
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Table 2.
Listed S
10. Tnxii I sed in (lie Analyses of Direct and Indirect K ITects lor the Assessed
)ecies
Listed
Species
Birds'
Mil iiiin;ils
Terrestrial
I'lillllS
Terrestrial
1 n\oris.
1-rcslm alcr
lislr
l-rcslmalcr
ln\crls.
Aquatic
I'lillllS
CRLF
Direct
Indirect
(prey)
Indirect
(prey)
Indirect
(habitat)
Indirect
(prey)
Direct
Indirect
(prey)
Indirect
(prey)
Indirect
(food/
habitat)
AW
Direct
Indirect
(prey)
Indirect
(prey)
Indirect
(habitat)
Indirect
(prey)
N/A
N/A
N/A
1 Birds are used as surrogates for the terrestrial-phase CRLF and for the AW.
2 Fish are used as surrogates for the aquatic-phase CRLF.
N/A = Not applicable
Table 2.11 Taxa and Assessment Kndpoinls I sed to Kvaliiate the Potential lor the I se of 2.4-1) to
Uesnll in Direct :ind Indirect K fleets to the ( KI.I- nntl the AW
Taxa I sod to Assess
Direct iiiul/or liuliivcl
HITocls lo Assessed
Species
Assessed Listed
Species
Mesisures til' l-'.colo^iciil l-'.ITecls1
1. Freshwater Fish and
Aquatic-phase
Amphibians
Direct Effect
Aquatic-phase CRLF
Survival, growth, and
reproduction of individuals
via direct effects
Acid/Salts
la. Common carp acute LC50
lb. Fathead minnow chronic NOAEC
Esters
lc. Bluegill sunfish acute LC50
Indirect Effect fprev)
Aquatic-phase and
Terrestrial-phase CRLF
Survival, growth, and
reproduction of individuals
via indirect effects on
aquatic prey food supply
(i.e., fish and aquatic-phase
amphibians)
2. Freshwater
Invertebrates
Indirect Effect (orev)
Aquatic-phase and
Terrestrial-phase CRLF
Survival, growth, and
reproduction of individuals
via indirect effects on
aquatic prey food supply
(i.e., freshwater
invertebrates)
Acid/Salts
2a. Daphnid acute EC50
2b. Daphnid chronic NOAEC
Esters
2c. Daphnid acute EC50
3. Aquatic Plants
(freshwater)
Indirect Effect
(food/habitat)
Aquatic-phase CRLF
Survival, growth, and
reproduction of individuals
via indirect effects on
habitat, cover, food supply,
and/or primary productivity
(i.e., aquatic plant
community)
Acid/Salts
5a. Water Milfoil EC50 (vascular plant)
5b. Navicula pelliculosa EC50 (freshwater
diatom)
Esters
5c. Duckweed EC50 (vascular plant)
5d. Skeletonema costatum EC50 (marine
diatom)
4. Birds
Direct Effect
Terrestrial-phase CRLF
AW
Survival, growth, and
reproduction of individuals
via direct effects
Acid/Salts/Esters
6a. Bobwhite quail gavage acute LD50 &
Bobwhite quail and mallard dietary acute
LC50
6b. Bobwhite quail chronic NOAEC
64
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Table 2.11 Taxa and Assessment Kndpoints I sed to Kvaluale (lie Potential lor (lie I se of 2.4-1) lo
Uesnll in Direct and Indirect KITecls lo the CUM'' and the AW
Ta\a I sed (o Assess
Direct and/or Indirect
F. fleets lo Assessed
Species
Species
Measures of Fcolo^ical t!ITecis1
Indirect Effect (orev)
Terrestrial-phase CRLF
AW
Survival, growth, and
reproduction of individuals
via indirect effects on
terrestrial prey (birds)
5. Mammals
Indirect Effect
(orcy/habitat from
burrows)
Terrestrial-phase CRLF
AW
Survival, growth, and
reproduction of individuals
via indirect effects on
terrestrial prey (mammals)
Acid/Salts/Esters
7a. Laboratory rat acute LD50
7b. Laboratory rat chronic NOAEC
6. Terrestrial
Invertebrates
Indirect Effect (orev)
Terrestrial-phase CRLF
AW
Survival, growth, and
reproduction of individuals
via indirect effects on
terrestrial prey (terrestrial
invertebrates)
Acid/Salts/Esters
8a. Honey bee acute LD50
7. Terrestrial Plants
Indirect Effect
(food/habitat) (non-
obi iaatc relationship)
Terrestrial-phase CRLF
AW
Survival, growth, and
reproduction of individuals
via indirect effects on food
and habitat (i.e., riparian
and upland vegetation)
Acid/Salts/Esters
9a. Monocot EC25: onion (seedling
emergence and vegetative vigor)
9b. Dicot EC25: tomato (seedling
emergence) and lettuce (vegetative vigor)
1 Toxicity data for the nine technical formulations of 2,4-D were bridged according to the taxonomic group, and the chemical
composition (acid, salt, ester). The summaries here reflect this established bridging strategy. More background and details are
found in Section 1, Section 2.2, and Section 4.2. The species listed is the most sensitive within each classification (acid/salts,
esters, or acid/salts/esters).
2.8.3 Assessment Endpoints for Designated Critical Habitat
As previously discussed, designated critical habitat is assessed to evaluate actions related
to the use of 2,4-D that may alter the PCEs of the assessed species' designated critical
habitats. PCEs for the assessed species were previously described in Section 2.6.
Actions that may modify critical habitat are those that alter the PCEs and jeopardize the
continued existence of the assessed species. Therefore, these actions are identified as
assessment endpoints. It should be noted that evaluation of PCEs as assessment
endpoints is limited to those of a biological nature {i.e., the biological resource
requirements for the listed species associated with the critical habitat) and those for
which 2,4-D effects data are available.
Some components of these PCEs are associated with physical abiotic features {e.g.,
presence and/or depth of a water body, or distance between two sites), which are not
expected to be measurably altered by use of pesticides. Measures of ecological effect
used to assess the potential for adverse modification to the critical habitat of the CRLF
and AW are described in Table 2.12.
65
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Table 2.12 Sum 111:1 rv of Assessment K ml points ami Measures of Ideological KITeel for
Primary Constituent Klenients of Designated Critical Habitat for CUM'' ami AW
1 :i\oii I sod lo
Assess Modification
of per.
Assessed Listed Species
Associated \\ ilh I lie
P( 1.
Measures of Ideological
I! Heels'
1. Freshwater Fish
and Aquatic-phase
Amphibians
Direct Effect
Aquatic-phase CRLF
Survival, growth, and
reproduction of
individuals via direct
effects
Acid/Salts
la. Rainbow trout acute LC50
lb. Fathead minnow chronic
NOAEC
Esters
lc. Bluegill sunfish acute LC50
Indirect Effect (orev)
Aquatic-phase and
Terrestrial-phase CRLF
Modification of critical
habitat via change in
aquatic prey food supply
(i.e., fish and aquatic-
phase amphibians)
2. Freshwater
Invertebrates
Indirect Effect Corey)
Aquatic-phase and
Terrestrial-phase CRLF
Survival, growth, and
reproduction of
individuals via indirect
effects on aquatic prey
food supply (i.e.,
freshwater invertebrates)
Acid/Salts
2a. Daphnid acute EC50
2b. Daphnid chronic NOAEC
Esters
2c. Daphnid acute EC50
3. Aquatic Plants
(freshwater)
Indirect Effect
(food/habitat)
Aquatic-phase CRLF
Modification of critical
habitat via change in
habitat, cover, food
supply, and/or primary
productivity (i.e., aquatic
plant community)
Acid/Salts
3 a. Water Milfoil EC50
(vascular plant)
3b. Navicula pel lieu losa EC50
(freshwater diatom)
Esters
3c. Duckweed EC50 (vascular
plant)
3d. Skeletonema costatum
EC50 (marine diatom)
4. Birds
Direct Effect
Terrestrial-phase CRLF
AW
Survival, growth, and
reproduction of
individuals via direct
effects
Acid/S alts/Esters
4a. Bobwhite quail gavage
acute LD50 & Bobwhite quail
and mallard dietary acute LC50
4b. Bobwhite quail chronic
NOAEC
Indirect Effect Corey)
Terrestrial-phase CRLF
AW
Modification of critical
habitat via change in
terrestrial prey (birds)
5. Mammals
Indirect Effect
(orcy/habitat from
burrows)
Terrestrial-phase CRLF
AW
Modification of critical
habitat via change in
terrestrial prey
(mammals)
Acid/Salts/Esters
5a. Laboratory rat acute LD50
5b. Laboratory rat chronic
NOAEC
6. Terrestrial
Invertebrates
Indirect Effect (orev)
Terrestrial-phase CRLF
AW
Modification of critical
habitat via change in
terrestrial prey (terrestrial
invertebrates)
Acid/S alts/Esters
6a. Honey bee acute LD50
66
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Table 2.12 Summary of Assessment Kndpoints and Measures of Ideological KITect lor
Primary Constituent Klements of Designated Critical llahitat for CUI.K and AW
1 :i\oii I sod Ki
Assess Modification
of PCI'.
Assessed l.isled Species
Associnlcd w illi (lie
P( 1.
Measures of Mcolo^icid
r.lTeds1
7. Terrestrial Plants
Indirect Effect
(food/habitat) (non-
oblisate relationship)
Terrestrial-phase CRLF
AW
Modification of critical
habitat via change in food
and habitat (i.e., riparian
and upland vegetation)
Acid/S alts/Esters
7a. MonocotEC25: onion
(seedling emergence and
vegetative vigor)
7b. Dicot EC25: tomato
(seedling emergence) and
lettuce (vegetative vigor)
toxicity data for the nine technical formulations of 2,4-D were bridged according to the taxonomic group, and
the chemical composition (acid, salt, ester). The summaries here reflect this established bridging strategy. More
background and details are found in Section 1, Section 2.2, and Section 4.2. The species listed is the most
sensitive within each classification (acid/salts, esters, or acid/salts/esters).
2.9 Conceptual Model
2.9.1 Risk Hypotheses
Risk hypotheses are specific assumptions about potential adverse effects {i.e., changes in
assessment endpoints) and may be based on theory and logic, empirical data,
mathematical models, or probability models (U.S. EPA, 1998). For this assessment, the
risk is stressor-linked, where the stressor is the release of 2,4-D to the environment. The
following risk hypotheses are presumed for each assessed species in this assessment:
The labeled use of 2,4-D within the action area may:
directly affect the CRLF and/or AW by causing mortality or by adversely
affecting growth or fecundity;
indirectly affect the CRLF and/or AW by modifying the designated critical habitat
by reducing or changing the composition of food supply;
indirectly affect the CRLF by modifying the designated critical habitat by
reducing or changing the composition of the aquatic plant community in the species'
current range, thus affecting primary productivity and/or cover;
indirectly affect the CRLF and/or AW by modifying the designated critical habitat
by reducing or changing the composition of the terrestrial plant community in the
species' current range;
indirectly affect the CRLF by modifying the designated critical habitat by
reducing or changing aquatic habitat in their current range (via modification of water
quality parameters, habitat morphology, and/or sedimentation);
modify the designated critical habitat of the CRLF by reducing or changing
upland habitat within 200 ft of the edge of the riparian vegetation necessary for shelter,
foraging, and predator avoidance;
67
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modify the designated critical habitat of the CRLF by reducing or changing
dispersal habitat within designated units and between occupied locations within 0.7 mi of
each other that allow for movement between sites including both natural and altered sites
which do not contain barriers to dispersal.
2.9.2 Diagram
The conceptual model is a graphic representation of the structure of the risk assessment.
It specifies the 2,4-D release mechanisms, biological receptor types, and effects endpoints
of potential concern. The conceptual models for aquatic and terrestrial phases of the
CRLF and AW and the conceptual models for the aquatic and terrestrial PCE components
of critical habitats are shown in Figures 2.5 and 2.6. Although the conceptual models for
direct/indirect effects and modification of designated critical habitat PCEs are shown on
the same diagrams, the potential for direct/indirect effects and modification of PCEs will
be evaluated separately in this assessment. Exposure routes shown in dashed lines are
not quantitatively considered because the contribution of those potential exposure routes
to potential risks to the CRLF and AW and modification to designated critical habitats is
expected to be negligible.
Stressor
Long range
atmospheric
transport
¦] Spray drift [¦
| Runoff"|
Source
S "L
Dermal uptake/lngestion-
Exposure
Media
Root uptake
Wet/dry depositions-
Ingestion
Ingestion
Ingestion
Ingestion
Ingestion
Receptors
Attribute
Change
Mammals/
birds
Terrestrial
insects
Soil
Direct
application
Terrestrial-phase
amphibians
Birds/terrestrial-
phase amphibians/
reptiles/mammals
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Food chain
Reduction in prey
Modification of PCEs
related to prey availability
Terrestrial/riparian plants
grasses/forbs, fruit, seeds
(trees, shrubs)
Pesticide applied to use site
Habitat integrity
Reduction in primary productivity
Reduced cover
Community change
Vlodification of PCEs related
to habitat
Figure 2.5 Conceptual Model for Terrestrial-Phase of the CRLF and AW
(applicable to the acid, salt, and ester technical formulations of 2,4-D)
68
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Stressor
~I Groundwater
Long range !
atmospheric !
transport j
Source
Spray drift
Exposure
Media
Wet/dry deposition
Uptake/gills
or integument
Uptake/cell,
roots, leaves
Uptake/gills
or integument
Receptors
Ingestion
Ingestion
r 1
Habitat integrity
Reduction in primary productivity
Reduced cover
Community change
Modification of PCEs related to
habitat
Attribute
Change
Runoff
Soil
Aquatic Plants
Non-vascular
Vascular
Aquatic Animals
Invertebrates
Vertebrates
Riparian plant
terrestrial
exposure
pathways see
Figure 2.5
Surface water/
Sediment
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Fish/aquatic phase
amphibians
^Piscivorous
mammals and birds
Food chain
Reduction in algae
Reduction in prey
Modification of PCEs
related to prey availability
Pesticide applied to use site
"Route of exposure includes only ingestion of aquatic fish and invertebrates
Figure 2.6a Conceptual Model for Aquatic-Phase of the CRLF (applicable to the
acid and salt technical formulations of 2,4-D, also applicable to ester technical forms
of 2,4-D for acute exposure (assuming all the ester has hydrolyzed to the acid prior
to reaching the water body) and for chronic exposure.
69
-------
Stressor
»| Groundwater
Long range !
atmospheric !
transport ;
Source
Spray drift
Exposure
Media
Wet/dry deposition
Uptake/gills
or integument
Uptake/cell,
roots, leaves
Uptake/gills
or integument
Receptors
Ingestion
Ingestion
i--L
XI
Habitat integrity
Reduction in primary productivity
Reduced cover
Community change
Modification of PCEs related to
habitat
Attribute
Change
Runoff
Soil
Aquatic Plants
Non-vascular
Vascular
Aquatic Animals
Invertebrates
Vertebrates
Riparian plant
terrestrial
exposure
pathways see
Figure 2.5
Surface water/
Sediment
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Fish/aquatic phase
amphibians
^Piscivorous
mammals and birds
Food chain
Reduction in algae
Reduction in prey
Modification of PCEs
related to prey availability
Pesticide applied to use site
"Route of exposure includes only ingestion of aquatic fish and invertebrates
Figure 2.6b Conceptual Model for Aquatic-Phase of the CRLF (applicable to the
ester technical formulations of 2,4-D, assuming ester has not yet hydrolyzed at time
of exposure).
2.10 Analysis Plan
In order to address the risk hypothesis, the potential for direct and indirect effects to the
CRLF and AW, prey items, and habitat is estimated based on a taxon-level approach. In
the following sections, the use, environmental fate, and ecological effects of 2,4-D are
characterized and integrated to assess the risks. This is accomplished using a risk
quotient (ratio of exposure concentration to effects concentration) approach. Although
risk is often defined as the likelihood and magnitude of adverse ecological effects, the
risk quotient-based approach does not provide a quantitative estimate of likelihood and/or
magnitude of an adverse effect. However, as outlined in the Overview Document (U.S.
EPA, 2004), the likelihood of effects to individual organisms from particular uses of 2,4-
D is estimated using the probit dose-response slope and either the level of concern
(discussed below) or actual calculated risk quotient value.
70
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2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model
2.10.1.1 Measures of Exposure
The environmental fate properties of 2,4-D along with available monitoring data indicate
that runoff and spray drift are the principle potential transport mechanisms of 2,4-D to the
aquatic and terrestrial habitats of the CRLF and AW. In this assessment, transport of 2,4-
D through runoff and spray drift is considered in deriving quantitative estimates of 2,4-D
exposure to CRLF and AW, their prey, and their habitats.
Measures of exposure are based on aquatic and terrestrial models that predict estimated
environmental concentrations (EECs) of 2,4-D using maximum labeled application rates
and methods of application. The models used to predict aquatic EECs are the Pesticide
Root Zone Model coupled with the Exposure Analysis Model System (PRZM/EXAMS).
The model used to predict terrestrial EECs on food items is T-REX. The model used to
derive EECs relevant to terrestrial and wetland plants is TerrPlant. These models are
parameterized using relevant reviewed registrant-submitted environmental fate data.
PRZM (v3.12.2, May 2005) and EXAMS (v2.98.4.6, April 2005) are screening
simulation models coupled with the input shell pe5.pl (August 2007) to generate daily
exposures and l-in-10 year EECs of 2,4-D that may occur in surface water bodies
adjacent to application sites receiving 2,4-D through runoff and spray drift. PRZM
simulates pesticide application, movement, and transformation on an agricultural field
and the resultant pesticide loadings to a receiving water body via runoff, erosion, and
spray drift. EXAMS simulates the fate of the pesticide and resulting concentrations in
the water body. The standard scenario used for ecological pesticide assessments assumes
application to a 10-hectare agricultural field that drains into an adjacent 1-hectare water
body, 2-meters deep (20,000 m3 volume) with no outlet. PRZM/EXAMS was used to
estimate screening-level exposure of aquatic organisms to 2,4-D. The measure of
exposure for aquatic species is the l-in-10 year return peak or rolling mean concentration.
The 1-in-10-year 60-day mean is used for assessing chronic exposure to fish; the 1-in-10-
year 21-day mean is used for assessing chronic exposure for aquatic invertebrates.
For the rice use, the Tier I rice model was used to estimate aquatic EECs. The model
assumes partitioning of the pesticide between water and the upper 1 cm of sediment but
does not include degradation. For the direct applications to water (e.g., ditchbanks and
water bodies), aquatic EECs were modeled using aerobic aquatic degradation rates.
Exposure estimates for the terrestrial animals assumed to be in the target area or in an
area exposed to spray drift are derived using the T-REX model (version 1.4.1, October 8,
2008). This model incorporates the Kenega nomograph, as modified by Fletcher et al.
(1994), which is based on a large set of actual field residue data. The upper limit values
from the nomograph represented the 95th percentile of residue values from actual field
measurements (Hoerger and Kenega, 1972).
71
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For modeling purposes, direct exposures of the CRLF and AW to 2,4-D through
contaminated food are estimated using the EECs for the small bird (20 g) which
consumes small insects. Dietary-based and dose-based exposures of potential prey (small
mammals) are assessed using the small mammal (15 g) which consumes short grass. The
small bird (20 g) consuming small insects and the small mammal (15 g) consuming short
grass are used because these categories represent the largest RQs of the size and dietary
categories in T-REX that are appropriate surrogates for the CRLF and AW and one of
their prey items. Estimated exposures of terrestrial insects to 2,4-D are bound by using
the dietary based EECs for small insects and large insects.
Birds are currently used as surrogates for terrestrial-phase amphibians and reptiles.
However, amphibians and reptiles are poikilotherms (body temperature varies with
environmental temperature) while birds are homeotherms (temperature is regulated,
constant, and largely independent of environmental temperatures). Therefore,
amphibians and reptiles tend to have much lower metabolic rates and lower caloric intake
requirements than birds or mammals. As a consequence, birds are likely to consume
more food than amphibians and reptiles on a daily dietary intake basis, assuming similar
caloric content of the food items. Therefore, the use of avian food intake allometric
equation as a surrogate to amphibians and reptiles is likely to result in an over-estimation
of exposure and risk for reptiles and terrestrial-phase amphibians. Therefore, T-REX has
been refined to the T-HERPS model (v. 1.0), which allows for an estimation of food
intake for poikilotherms using the same basic procedure as T-REX to estimate avian food
intake.
EECs for terrestrial plants inhabiting dry and wetland areas are derived using TerrPlant
(version 1.2.2, December 26, 2006). This model uses estimates of pesticides in runoff
and in spray drift to calculate EECs. EECs are based upon solubility, application rate and
minimum incorporation depth.
The spray drift model, AgDRIFT is used to assess exposure to 2,4-D deposited on terrestrial
habitats by spray drift. In addition to the buffered area from the spray drift analysis, the
downstream extent of 2,4-D that exceeds the LOC for the effects determination is also
considered.
2.10.1.2 Measures of Effect
Data identified in Section 2.10 are used as measures of effect for direct and indirect
effects to the CRLF and AW. Data were obtained from registrant-submitted studies or
from literature studies identified by ECOTOX. The ECOTOXicology database
(ECOTOX) was searched in order to provide more ecological effects data and in an
attempt to bridge existing data gaps. ECOTOX is a source for locating single chemical
toxicity data for aquatic life, terrestrial plants, and wildlife. ECOTOX was created and is
maintained by the U.S. EPA, Office of Research and Development, and the National
Health and Environmental Effects Research Laboratory's Mid-Continent Ecology
Division.
72
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The assessment of risk for direct effects to the terrestrial-phase CRLF and AW makes the
assumption that toxicity of 2,4-D to birds is similar to or less than the toxicity to
terrestrial-phase amphibians and reptiles (this also applies to potential prey items). The
same assumption is made for fish and aquatic-phase CRLF (again, this also applies to
potential prey items).
The acute measures of effect used for animals in this screening level assessment are the
LD50, LC50, and EC50. LD stands for "Lethal Dose", and LD50 is the amount of a
material, given all at once, that is estimated to cause the death of 50% of the test
organisms. LC stands for "Lethal Concentration" and LC50 is the concentration of a
chemical that is estimated to kill 50% of the test organisms. EC stands for "Effective
Concentration" and the EC50 is the concentration of a chemical that is estimated to
produce a specific effect in 50% of the test organisms. Endpoints for chronic measures of
exposure for listed and non-listed animals are the NOAEL/NOAEC and NOEC. NOAEL
stands for "No Ob served-Adverse-Effect-Level" and refers to the highest tested dose of a
substance that has been reported to have no harmful (adverse) effects on test organisms.
The NOAEC {i.e., "No-Observed-Adverse-Effect-Concentration") is the highest test
concentration at which none of the observed effects were statistically different from the
control. The NOEC is the No-Observed-Effects-Concentration. For non-listed plants,
only acute exposures are assessed {i.e., EC25 for terrestrial plants and EC50 for aquatic
plants).
It is important to note that the measures of effect for direct and indirect effects to the
assessed species and their designated critical habitat are associated with impacts to
survival, growth, and fecundity, and do not include the full suite of sublethal effects used
to define the action area. According the Overview Document (U.S. EPA, 2004), the
Agency relies on effects endpoints that are either direct measures of impairment of
survival, growth, or fecundity or endpoints for which there is a scientifically robust, peer
reviewed relationship that can quantify the impact of the measured effect endpoint on the
assessment endpoints of survival, growth, and fecundity.
2.10.1.3 Integration of Exposure and Effects
Risk characterization is the integration of exposure and ecological effects characterization
to determine the potential ecological risk from agricultural and non-agricultural uses of
2,4-D, and the likelihood of direct and indirect effects to CRLF and AW in aquatic and
terrestrial habitats. The exposure and toxicity effects data are integrated in order to
evaluate the risks of adverse ecological effects on non-target species. For the assessment
of 2,4-D risks, the risk quotient (RQ) method is used to compare exposure and measured
toxicity values. EECs are divided by acute and chronic toxicity values. The resulting
RQs are then compared to the Agency's levels of concern (LOCs) (U.S. EPA, 2004) (see
Appendix I).
For this endangered species assessment, listed species LOCs are used for comparing RQ
values for acute and chronic exposures of 2,4-D directly to the CRLF and AW. If
estimated direct exposures to the assessed species of 2,4-D resulting from a particular use
73
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are sufficient to exceed the listed species LOC, then the effects determination for that use
is "may affect". When considering indirect effects to the assessed species due to effects
to prey, the listed species LOCs are also used. If estimated exposures to the prey of the
assessed species of 2,4-D resulting from a particular use are sufficient to exceed the listed
species LOC, then the effects determination for that use is a "may affect." If the RQ
being considered also exceeds the non-listed species acute risk LOC, then the effects
determination is a LAA. If the acute RQ is between the listed species LOC and the non-
listed acute risk species LOC, then further lines of evidence {i.e., probability of individual
effects, species sensitivity distributions) are considered in distinguishing between a
determination of NLAA and a LAA. If the RQ being considered for a particular use
exceeds the non-listed species LOC for plants, the effects determination is "may affect".
Further information on LOCs is provided in Appendix I.
2.10.2 Data Gaps
2.10.2.1 Fate and Transport Data
The registrant-submitted fate and transport data (classified as either Acceptable or
Supplemental) provide sufficient information for EFED to identify 2,4-D routes of
dissipation in surface soils and water and, therefore, were sufficient to conduct the risk
assessment. No apparent data gaps were identified in the fate and transport database.
The summaries of environmental fate studies of 2,4-D are presented in Appendix B.
2.10.2.2 Ecotoxicity Data
The registrant-submitted ecotoxicity data and open literature ECOTOX data (classified as
either Acceptable or Supplemental) provide sufficient information for EFED to identify
2,4-D routes of exposure to aquatic and terrestrial organisms. No apparent data gaps
were identified in the ecotoxicity database. The summaries of environmental effects
studies of 2,4-D are presented in Appendix F.
3. Exposure Assessment
3.1 Label Application Rates and Intervals
Crop-specific management practices for all of the assessed uses of 2,4-D were used for
modeling, including application rates, number of applications per year, application
intervals, and the first application date for each crop (Table 3.1). The date of first
application was developed based on several sources of information including data
provided by BEAD, a summary of individual applications from the CDPR PUR data, and
Crop Profiles maintained by the USD A. More detail on the crop profiles may be found at
http://www.ipmcenters.org/CropProfiles/. As depicted in Figure 3.1, most of the 2,4-D
applications were made in the first quarter of the year from 1999 to 2006.
74
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Tsihle 3.1 2.4-1) I scs Assessed lor CModeling Scenario. Application Usiles nnd Timing
Masler l.ahel I se
( alexin iiiid Detailed
'ises'
2.4-1) l-orins lor
\\ liicli (lie I se is
Labeled
PU/.\l/r.XA\lS
Scenario
(first app da(c)
Mclhod:
Application Kale
(intcr\al hclwccn applications)
Orchard Uses
Nut Orchards,
Pistachios
Acid, DMA, TIP A,
IP A, DEA, Na
CA Almond wirrig STD
(10-Feb)
G
2 apps @ 2 lb a.e./acre
(30-day interval)
Filberts
Acid, DMA, TIP A,
IP A, DEA, Na
CA Almond wirrig STD
(10-Feb)
G
4 apps @ 0.5 lb a.e./acre3
(30-day interval)
Grapes
Acid, DMA, TIP A,
IP A, DEA, Na
CA Grapes STD
(1-Mar)
G
1 app @ 1.36 lb a.e./acre
Grapes (wine grapes)
Acid, DMA, TIP A,
IP A, DEA, Na
CA Wine Grapes RLF
(1-Mar)
G
1 app @ 1.36 lb a.e./acre
Blueberries
Acid, DMA, TIP A,
IP A, DEA, Na
CA Wine Grapes RLF
(5-Mar)
G
1 post-emergence app @ 1.4 lb
a.e./acre and 1 post-harvest app @
1.4 lb a.e./acre
Stone and Pome Fruits
Acid, DMA, TIP A,
IP A, DEA, Na
CA Fruit wirrig STD
(1-Mar)
G
2 apps @ 2 lb a.e./acre
(7 5-day interval)
Citrus
IPE
CA Citrus STD
(1-Mar)
G
1 app (i 0,1 lb a.e./acre
A
1 app (3> 0.1 lb a.e./acre
Agricultural - Food Crop Uses
Field Corn, Popcorn
Acid, DMA, TIP A,
IP A, DEA, Na, 2-EHE,
BEE
CA Corn OP
(15-Mar)
G
1 app @ 1.0 lb a.e./acre March 15,
1 app @ 0.5 lb a.e./acre April 29
1 app @ 1.5 lb a.e./acre August 15
(pre-harvest)
A
1 app @ 1.0 lb a.e./acre March 15,
1 app @ 0.5 lb a.e./acre April 29
1 app @ 1.5 lb a.e./acre August 15
(pre-harvest)
Sweet Corn
Acid, DMA, TIP A,
IP A, DEA, Na, 2-EHE,
BEE
CA Corn OP
(15-Mar)
G
1 app @ 1 lb a.e./acre March 15; 1
app (i 0.5 lb a.e./acre April 29
A
1 app @ 1 lb a.e./acre on March 15;
and 1 app @ 0.5 lb a.e./acre on April
29
Potatoes
Fresh market only
Acid, DMA, TIP A,
IP A, DEA, Na, 2-EHE,
BEE
CA Potato RLF
(1-Apr)
G
2 apps @ 0.07 lb a.e./acre
(10-day interval)
A
2 apps @ 0.07 lb a.e./acre
(10-day interval)
Sugarcane4
Acid, DMA, TIP A,
IP A, DEA, Na
CA Sugar beet wirrig OP
(20-Jan)
G
1 pre-emergence and 1 post-
emergence app @ 2 lb a.e./acre
(20-day interval)
A
1 pre-emergence and 1 post-
emergence app @ 2 lb a.e./acre
(20-day interval)
Cereal Grains
Wheat, Barley, Millet,
Oats, Rye
Acid, DMA, TIP A,
IP A, DEA, Na, 2-EHE,
BEE
CA Wheat RLF
(10-Feb)
G
1 post-emergence app @ 1.25 lb
a.e./acre and 1 pre-harvest app @ 0.5
lb a.e./acre
(90-day interval)
A
1 post-emergence app @ 1.25 lb
a.e./acre and 1 pre-harvest app @ 0.5
lb a.e./acre
(90-day interval)
75
-------
Tsihlc 3.1 2.4-1) I scs Assessed lor ( nlilbrni;!. Modeling Scensirio. Application Usiles nnd 'Mining
Master Label I sc
(alcgon iiiid Detailed
I scs1
2.4-1) l-'orms for
\\ liich (lie I sc is
1 abclcd
PR/.M/I.WMS
Scenario
(first app dale)
Method2
Application Kale
(inlcnal between applicalions)
Grain or Forage
Sorghum
Acid, DMA, TIP A,
IP A, DEA, Na
CA Wheat RLF
(10-Feb)
G
1 post-emergence app @ 1.0 lb
a.e./acre
A
1 post-emergence app @ 1.0 lb
a.e./acre
2-EHE, BEE
CA Wheat RLF
(10-Feb)
G
1 post-emergence app @ 0.5 lb
a.e./acre
A
1 post-emergence app @ 0.5 lb
a.e./acre
Hops
Acid, DMA, TIP A,
IP A, DEA, Na
OR hops STD
(10-Apr)
G
3 apps @ 0.5 lb a.e./acre
(30-day interval)
A
3 apps @ 0.5 lb a.e./acre
(30-day interval)
Asparagus
Acid, DMA, TIP A,
IP A, DEA, Na
CA Row Crop RLF
(1-Apr)
G
2 apps @ 2 lb a.e./acre
(30-day interval)
A
2 apps @ 2 lb a.e./acre
(30-day interval)
Fallowland and Crop
Stubble
Acid, DMA, TIP A,
IP A, DEA, Na, 2-EHE,
BEE
CA Row Crop RLF
(1-Aug)
G
2 apps @ 2 lb a.e./acre
(30-day interval)
A
2 apps @ 2 lb a.e./acre
(30-day interval)
Agricultural - Non-food Crop Uses
Established Grass
Pastures, Rangeland,
Perennial Grassland
Not in Agricultural
Production
Acid, DMA, TIP A,
IP A, DEA, Na, 2-EHE,
BEE
CA Rangeland Hay RLF
(1-Mar)
G
2 apps @ 2 lb a.e./acre
(30-day interval)
Non-agricultural Uses
Non-cropland
Fencerows, Hedgerows,
Roadsides, Ditches,
Rights-of-way, Utility
power lines, Railroads,
Airports, Industrial
sites, and Other non-
crop areas
Acid, DMA, TIP A,
IP A, DEA, Na, 2-EHE,
BEE
CA Right-of-Way RLF
(20-Feb)
G
1 app (i 4 lb a.e./acre
A
1 app @ 4 lb a.e./acre
Forestry
Forest site preparation,
Forest roadsides, Brush
control, Established
conifer release
including Christmas
trees and reforestation
areas
Acid, DMA, TIP A,
IP A, DEA, Na, 2-EHE,
BEE
CA Forestry RLF
(1-Mar)
G
1 app (i 4 lb a.e./acre
A
1 app @ 4 lb a.e./acre
Tree and Brush
Acid, DMA, TIP A,
CA Forestry RLF
G
1 app @ 4 lb a.e./acre
76
-------
Tsihlc 3.1 2.4-1) I scs Assessed lor ( nlilbrni;!. Modeling Soensirio. Application Usiles nnd 'Mining
Master l.ahcl I sc
(alciion iiiid Detailed
I scs1
2.4-1) l-'orms for
\\ liich (lie I se is
1 ahclcd
PR/.M/IAAMS
Scenario
(firsl app dale)
Method2
Application Kale
(inlcnal between applications)
Control
Alder, Ash, Aspen,
Birch, Blackgum,
Cherry, Elm, Oak,
Sweetgum, Tulip
poplar, Willow, and
Others
IP A, DEA, Na, 2-EHE,
BEE
(1-Mar)
A
1 app @ 4 lb a.e./acre
Ornamental Turf
Golf courses,
Cemeteries, Parks,
Sports fields, Turfgrass,
Lawns and other grass
areas
Acid, DMA, TIP A,
IP A, DEA, Na, 2-EHE,
BEE
CA Turf RLF
(1-Mar)
G
2 apps @ 1.5 lb a.e./acre
(21-day interval)
A
2 apps @ 1.5 lb a.e./acre
(21-day interval)
Grass Grown for Seed
and Sod
Acid, DMA, TIP A,
IP A, DEA, Na, 2-EHE,
BEE
CA Turf RLF
(1-Mar)
G
2 apps @ 2 lb a.e./acre
(21-day interval)
A
2 apps @ 2 lb a.e./acre
(21-day interval)
Direct Application to Water Uses
Rice
Acid, DMA, TIP A,
IP A, DEA, Na
Direct water application
(Rice model)5
G & A
1 app @ 1.5 lb a.e./acre
Aquatic Weed Control
Surface application or
subsurface injection for
submersed weeds
Acid, DMA, TIP A,
IP A, DEA, Na, BEE
Direct water application
(Modeled using aerobic
aquatic degradation rates)5
G & A
1 app @ 10.8 lb a.e./acre foot
Aquatic Weed Control
Irrigation ditchbank
application
Acid, DMA, TIP A,
IP A, DEA, Na, BEE
Direct water application
(Modeled using aerobic
aquatic degradation rates)5
G & A
2 app @ 2.0 lb a.e./acre
(30-day interval)
Aquatic Weed Control
Surface application for
floating and emergent
aquatic weeds
Acid, DMA, TIP A,
IP A, DEA, Na, BEE
Direct water application
(Modeled using aerobic
aquatic degradation rates)5
G & A
2 app @ 4.0 lb a.e./acre
(21-day interval)
'Uses are derived from Master Label for Reregistration of 2,4-Dichlorophenoxyacetic Acid Uses - Supported by the 2,4-D
Industry and IR-4.
2G = ground application. A = aerial application.
3The Master Label indicates a maximum single application rate of 1.0 lb a.e./lOO gallons spray for filberts, SRRD verified that
this rate is equivalent to a maximum single application rate of 0.5 lb a.e./acre, which represents a conservative estimate.
4Because EFED does not currently have a PRZM/EXAMS scenario for CA Sugarcane, sugarcane uses were modeled using the
CA Sugar beet scenario as a surrogate.
5Details of the aquatic modeling and EEC estimation for direct application to water uses are discussed in Sections 3.2.3 and
3.2.4.
77
-------
Total Lbs Used by Week for 2,4-D (production)
180000
160000
140000
-------
Table 3.2 Summary of PUZM/KYVMS Modeling Inputs for 2.4-1) Acid
Kate Property
Value
Source
Photolysis in Water
13 days
MRID 41125306
Aerobic Soil Metabolism1
6.2 days
MRID 00116625
MRID 43167501
Hydrolysis
Stable
MRID 41007301
Aerobic Aquatic Metabolism
(water column)
45 days
MRID 42025301
MRID 42979201
MRID 44188601
Anaerobic Aquatic Metabolism
(benthic)2
231 days
MRID 43356001
O
o
61.7 mL/g
MRID 42045302
MRID 00112937
MRID 44117901
Chemical Application Method
(CAM)
1 for ground applications
2 for foliar applications
EFED Guidance4
Application Efficiency
0.99 for ground applications
0.95 for aerial applications
EFED Guidance
Spray Drift Fraction
0.01 for ground applications
0.05 for aerial applications
EFED Guidance
'Upper 90th Percentile based on acceptable aerobic metabolism half lives of 1.44, 2.92, 4.5, 12.4,
4.38, 1.99, and 1.7 days.
2Single value to multiply by 3
3Average Koc value
4Inputs determined in accordance withEFED "Guidance for Chemistry and Management Practice
Input Parameters for Use in Modeling the Environmental Fate and Transport of Pesticides" dated
February 28, 2002
3.2.2 Surface Water Modeling Approach and Inputs for 2,4-D Ester Drift
Only and Drift+Runoff (all scenarios except rice and direct water
applications)
EFED's strategy for bridging the fate data requirements for the ester and amine salt forms
of 2,4-D to the acid form was supported by laboratory data, which indicated rapid
conversion of the amine salt and ester forms of 2,4-D to the acid form. The sodium salt
form was considered to be equivalent to the acid form. However, it was noted at the time
of the establishment of the fate strategy that 2,4-D esters may persist under acidic aquatic
conditions. A condition of the establishment of the bridging strategy was that terrestrial
field dissipation studies should be conducted using 2,4-D DMA and 2,4-D EHE. Review
of the terrestrial field dissipation studies indicate that the study authors reported that 2,4-
D DMA converts rapidly to 2,4-D acid (in many instances, conversion occurred in the
tank mix), although it appears the analytical method may not have been able to detect
2,4-D DMA. The terrestrial field dissipation data for 2,4-D EHE indicate that the ester
79
-------
form may persist in the field for several days with half-lives ranging between 1 and 14
days and a median half-life of 2.9 days. In addition, the abiotic hydrolysis studies for the
2,4-D esters indicates that ester hydrolysis to 2,4-D acid is pH dependent with no
hydrolysis occurring under acid or neutral conditions (as an example 2,4-D EHE
hydrolyzes at pH 5 with a half-life of 99 days and the hydrolysis half-life at pH 7 is 48
days, while hydrolysis at pH 9 was 52 hours). However, hydrolysis soil slurry data
indicate that dissipation in a non-sterile water body will occur at all pHs, and published
literature indicates that 2,4-D esters in natural waters degrade rapidly with an average
half-life of less than 3 hours. Registrant sponsored research indicates the 2,4-D esters
(ethylhexyl, isopropyl, butylethyl) degrade rapidly (tin< 24 hours) in soil slurries,
aerobic aquatic environments, and anaerobic, acidic aquatic environments. Several field
studies show phenoxy herbicide esters are more persistent under extremely dry soil [<
soil wilting point (-15 bars)] conditions (Smith and Hay den, 1980; Smith, 1972;
Smith, 1976) while in moist soils [-50 to 80% field capacity (-0.3 bars)] and soil slurries,
phenoxy herbicide esters degraded rapidly (>85% degradation) during a 48 hour
incubation period. These degradation rates raise the concern of the impact of the drift of
the esters of 2,4-D to aquatic environments when spray is applied to terrestrial systems.
To address these concerns, two additional modeling approaches were utilized to account
for potential ester exposures in the aquatic environments. For uses that allow for 2,4-D
ester (BEE, EHE, or IPE) applications, a drift only scenario and a drift+runoff scenario
were modeled. Chronic EECs were not provided in this scenario because both registrant
and open literature data indicate that hydrolysis of the esters in a non-sterile water body
will occur at all pHs in a relatively short time frame (< 48 hours).
Drift of 2,4-D esters to the standard aquatic pond was modeled for each scenario
assuming 5% spray drift for aerial application and 1% spray drift for ground application
(as per EFED guidance). The amount of loading for each scenario was estimated by
converting the application rate (determined by reviewing ester labels only) to the drift
loading and multiplying the application amount (2.24 kilograms per hectare for turf) by
the drift (5% for aerial application). The resulting loading to the standard pond (0.112 kg
to the 1 hectare pond as an example) was converted to an acute concentration by dividing
the loading to the standard pond with a surface area of one hectare by the volume of the
pond (20,000,000 liters). The resulting concentration represents the maximum
instantaneous concentration predicted by direct drift from the application to the pond.
To account for the potential for runoff during the time in which 2,4-D EHE may remain
in the field, EFED conducted additional modeling with PRZM/EXAMS to assess the
potential for aquatic organisms to be exposed to 2,4-D EHE when applied to the same
terrestrial crops as modeled in the ester drift scenario. Model inputs for 2,4-D EHE are
listed in the Table 3.3. As with the drift only scenario, chronic EECs were not generated.
80
-------
1 able 3.3 PUZM/IAAMS Input Parameters for 2.4-1) INI.
Model Parameter
Value
Comments
Source
Aerobic Soil Metabolism
tl/2
24 days
estimated upper 90th
percentile 1
MRID 42059601
Aerobic Aquatic Degradation
t1/2 (KBACW)
48 days
2 x the aerobic soil
metabolism
degradation rate
Estimated per EFED
Guidance2
Anaerobic Aquatic Degradation
t1/2 (KBACS)
Stable
No data
Estimated per EFED
Guidance2
Aqueous Photolysis ti/2
128 days
MRID 42749702
Hydrolysis ti/2
48 days
MRID 42735401
Koc
10500 ml/g
Estimated by
EpiSuite Software
Molecular Weight
333.26
Product Chemistry
Water Solubility
0.32 mg/L
Product Chemistry
Vapor Pressure
4 57 x 10 6 mm
Hg
Product Chemistry
Henry's Law Constant
5.78 x 10"5 atm-
m3/mole
Product Chemistry
1 Three times (Upper 90th Percentile) based on single soil half life estimated from acceptable
laboratory volatility study of 8 days.
2 Fro in I Guidance for Chemistry and Management Practice Input Parameters for Use in Modeling
the Environmental Fate and Transport of Pesticides, dated at February 28, 2002.
3.2.3 Surface Water Modeling Approach and Inputs for Rice Scenario
The use of 2,4-D on rice was modeled using a Tier I approach developed by EFED. A
more complete discussion of the rice model may be found in the EFED policy
memorandum dated May 8, 2007. The model involves an assumption of uniform
application of pesticide to a rice paddy and calculates an EEC in the water column that
could potentially be released from the paddy. EFED guidance recommends using this
EEC for both acute and chronic exposures use on rice. For compounds that degrade
rapidly into degradates that are not of risk concern, the chronic EEC is expected to be
conservative. The formula of the Tier I Rice Model vl.O is as follows:
q "*ai
w ~ 0.00105 + 0.00013Kd
and, if appropriate:
Kd = 0.0LKoc
where:
Cw = water concentration [jug/L]
mai' = mass applied per unit area [kg/ha]
Kd = water-sediment partitioning coefficient [L/kg]
Koc = organic carbon partitioning coefficient [L/kg]
81
-------
2,4-D is registered for use in rice paddies for the acid and amine salt forms (esters are not
registered for rice use) with a maximum seasonal application rate of 1.5 lb a.e./A.
Modeling of this use rate results in an estimated 2,4-D concentration in the rice paddy of
1486 jig a.e./L, This model was calibrated to be conservative for most pesticides at the
edge of the paddy. The lack of consideration for degradation, dilution, and dispersion
may affect estimated concentrations downstream from the rice paddies. However, the
exact level of conservativeness has not been fully evaluated in the context of regionally-
dependent management practices, pesticide management practices, and universe of
pesticide fate properties. Once released from the paddy, the concentrations are expected
to decrease due to degradation, dilution, and dispersion.
The EEC derived by modeling 2,4-D use on rice is higher than concentrations detected in
the surface water monitoring data evaluated as part of this assessment. However,
analytical results of pond water after the direct application of 2,4-D reported in an aquatic
field dissipation study (MRID 43491601) on rice submitted by the registrant indicate that
initial concentrations (equivalent to the instantaneous estimate above) were as high as
2343 |ig a.e./L with a mean concentration reported as 1372 jag a.e./L, suggesting that the
model estimates are comparable to measured concentrations.
3.2.4 Surface Water Modeling Approach and Inputs for Direct Application
Scenario
Because there are no existing modeling scenarios for direct application to water, a first
approximation of an EEC was predicted assuming direct application to the standard pond.
For this assessment, EFED utilized a first-order decay model to estimate average
concentrations, which incorporates degradation based on an acceptable aerobic aquatic
metabolism study (ti/2 =15 days, used input value of 45 days per EFED Guidance) for the
EFED standard pond with no flow. EFED assumed that 2,4-D is uniformly applied to the
EFED standard pond with a surface area of 1 hectare and a volume of 20,000,000 liters.
Peak concentrations were determined using the target concentration (if provided in the
label) or by calculation based on application rate and pond volume assuming
instantaneous mixing of chemical. The 21-day average and 60-day average
concentrations were calculated assuming first-order dissipation from aerobic aquatic
degradation. An equation representing first-order decay was used to estimate average
concentrations:
C0x(\-e-kt)
concentration = -
kt
where: Co = initial concentration,
k = first-order aerobic aquatic degradation rate (= 0.00064),
t = time (in hours).
The interpretation of the label for aquatic weed control (surface application or subsurface
injection for submersed weeds) is that the target rate for 2,4-D use is based on
82
-------
concentration and not application rate. In order to account for this scenario, it was
assumed that 2,4-D would be applied at a rate to meet the target concentration of 4000
[j,g/L. This assumption would be applicable across all water bodies since the target rate is
based on a rate per acre foot of water (10.8 lb a.e./acre-foot) and would be independent of
water body geometry/volume. This scenario included the assumption of uniform
application across the entire water body. Modeling for this scenario predicts direct water
application of 2,4-D will yield surface water concentrations of 2,4-D in the EFED
standard pond of 4000 jig a.e./L for peak, 3417 jig a.e./L for the 21-day average, and
2610 (ig a.e./L for the 60-day average after a single application of 2,4-D. Although
multiple applications are permitted, only a single application was modeled. Therefore,
EECs would exceed those calculated in this assessment if multiple applications are made.
Other application scenarios in which water applications would occur are 'irrigation
ditchbanks' and 'surface application for floating and emergent aquatic weeds.'
Application rates for these uses are provided in lb a.e./acre, but were converted to a target
(peak) concentration by assuming a uniform water depth of one foot. Twenty-one-day
and 60-day average concentrations were calculated using the same formula as above
(aquatic weed control, surface application, or subsurface injection). Again, for these uses
multiple applications could be made in a calendar year; however, the EECs for only one
application were calculated.
3.2.5 Surface Water Modeling Results and Estimated Aquatic EECs
The aquatic EECs for 2,4-D for the various scenarios and application practices are listed
in Table 3.4. Two aquatic application scenarios with the highest peak water column
concentrations are direct application to control aquatic weeds (range from 740 to 4000 |ig
a.e./L) and rice (1431 [^g a.e./L). All other scenarios have peak concentrations less than
50 [^g a.e./L, with the lowest value less than 0.5 jag a.e./L for citrus use.
Results of the drift loading of the 2,4-D esters to the standard aquatic pond are presented
in Table 3.5. The 4 lb a.e./acre application rate predicts the highest peak concentrations
of 11.2 jag a.e./L and 2.2 |ig a.e./L, respectively for aerial applications and ground
applications.
Results of the drift+runoff loading of the 2,4-D esters to the standard aquatic pond are
presented in Table 3.5. The 4 lb a.e./acre application rate for forestry predicts the highest
peak concentrations of 13.24 jag a.e./L and 7.14 jag a.e./L for aerial applications and
ground applications, respectively.
83
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Table 3.4 Aquatic KKCs lor 2.4-1) Acid/Ssill I scs in C':ilil<>rni:i
Masler l.ahel
PRZM/r.WMS
Scenario
(I'irsl app dale)
\lellmd;
Application Kale
1.1
(jig a.e./l.)
I so ( alegon1
(inlcnal hclwccn applicalions)
Peak
21-da\
(>0-da\
Orchard Uses
Nut
Orchards,
Pistachios
CA Almond wirrig
STD
(10-Feb)
G
2 apps @ 2 lb a.e./acre
(30-day interval)
13.69
12.71
11.10
Filberts
CA Almond wirrig
STD
(10-Feb)
G
4 apps @ 0.5 lb a.e./acre3
(30-day interval)
4.06
3.77
3.38
Grapes
CA Grapes STD
(1-Mar)
G
1 app @ 1.36 lb a.e./acre
4.52
4.16
3.59
Grapes(wine
grapes)
CA Wine Grapes RLF
(1-Mar)
G
1 app @ 1.36 lb a.e./acre
2.94
2.70
2.34
Blueberries
CA Wine Grapes RLF
(5-Mar)
G
1 post-emergence app @ 1.4 lb
a.e./acre and 1 post-harvest app @
1.4 lb a.e./acre
3.15
2.93
2.58
Stone and
CA Fruit wirrig STD
n
2 apps @ 2 lb a.e./acre
6.98
6.35
5.30
Pome Fruits
(1-Mar)
(7 5-day interval)
Citrus6
CA citrus STD
A
1 app @ 0.1 lb a.e./acre
0.32
0.28
0.24
G
0.08
0.08
0.07
Agricultural - Food Crop Uses
1 app @ 1.0 lb a.e./acre March 15,
Field Corn,
CA Corn OP
A
1 app @ 0.5 lb a.e./acre April 29
1 app @ 1.5 lb a.e./acre August 15
(pre-harvest)
12.17
11.13
9.84
Popcorn
(15-Mar)
1 app @ 1.0 lb a.e./acre March 15,
G
1 app @ 0.5 lb a.e./acre April 29
1 app @ 1.5 lb a.e./acre August 15
(pre-harvest)
9.41
8.60
7.40
Sweet Corn
CA Corn OP
(15-Mar)
A
1 app @ 1 lb a.e./acre March 15; 1
app a 0.5 lb a.e./acre April 29
9.57
8.91
8.00
G
1 app @ 1 lb a.e./acre on March
15; and 1 app @ 0.5 lb a.e./acre on
April 29
7.41
6.90
6.00
Potatoes
CA Potato RLF
A
2 apps @ 0.07 lb a.e./acre
(10-day interval)
0.418
0.379
0.304
(1-Apr)
G
2 apps @ 0.07 lb a.e./acre
(10-day interval)
0.119
0.108
0.087
Sugarcane4
CA Sugar beet wirrig
OP
(20-Jan)
A
1 pre-emergence and 1 post-
emergence app (3> 2 lb a.e./acre
33.31
31.28
27.40
G
1 pre-emergence and 1 post-
emergence app (3> 2 lb a.e./acre
25.85
24.25
21.02
A
1 post-emergence app @ 1.25 lb
a.e./acre and 1 pre-harvest app @
0.5 lb a.e./acre
23.43
21.82
18.85
Cereal Grains
CA Wheat RLF
(90-day interval)
(10-Feb)
G
1 post-emergence app @ 1.25 lb
a.e./acre and 1 pre-harvest app @
0.5 lb a.e./acre
(90-day interval)
21.39
19.89
17.19
84
-------
Table 3.4 Aqunlic KKCs lor 2.4-1) Acid/Ssill I scs in ('sililorniii
Masler l.ahel
PK/.M/I.WMS
Scenario
(first app dale)
\lelhod:
Application Kale
1.1
(jig a.e./l.)
I se ( alegon 1
(inlcnal between applicalions)
Peak
21-daj
(>0-da\
Grain or
Forage
CA Wheat RLF
A
1 post-emergence app @ 1.0 lb
a.e./acre
18.61
17.33
14.96
Sorghum
(10-Feb)
G
1 post-emergence app @ 1.0 lb
a.e./acre
17.00
15.82
13.66
Hops
OR hops STD
A
3 apps @ 0.5 lb a.e./acre
(30-day interval)
4.62
4.19
3.69
(10-Apr)
G
3 apps @ 0.5 lb a.e./acre
(30-day interval)
1.73
1.55
1.33
Asparagus
CA Row Crop RLF
A
2 apps @ 2 lb a.e./acre
(30-day interval)
20.14
18.51
16.87
(1-Apr)
G
2 apps @ 2 lb a.e./acre
(30-day interval)
12.62
11.77
10.85
Fallow land
and Crop
Stubble
CA Row Crop RLF
A
2 apps @ 2 lb a.e./acre
(30-day interval)
10.70
9.70
8.32
(1-Aug)
G
2 apps @ 2 lb a.e./acre
(30-day interval)
2.16
1.95
1.69
Agricultural - Non-food Crop Uses
Established
Grass
Pastures,
Rangeland,
Perennial
Grassland
Not in
Agricultural
Production
CA Rangeland Hay
RLF
(1-Mar)
G
2 apps @ 2 lb a.e./acre
(30-day interval)
13.02
12.10
10.52
Non-agricultural Uses
CA Right-of-Way
A
1 app (i 4 lb a.e./acre
46.66
43.76
38.62
Non-cropland
RLF
(20-Feb)
G
1 app @ 4 lb a.e./acre
39.02
36.54
32.24
Forestry,
A
1 app (Si 4 lb a.e./acre
24.98
23.49
21.03
Tree and
Brush
Control
CA Forestry RLF
(1-Mar)
G
1 app @ 4 lb a.e./acre
15.92
14.99
13.42
Ornamental
CA Turf RLF
A
2 apps @ 1.5 lb a.e./acre
(21-day interval)
12.96
12.12
10.81
Turf
(1-Mar)
G
2 apps @ 1.5 lb a.e./acre
(21-day interval)
5.55
5.17
4.61
Grass Grown
for Seed and
Sod
CA Turf RLF
A
2 apps @ 2 lb a.e./acre
(21-day interval)
14.87
13.81
12.06
(1-Mar)
G
2 apps @ 2 lb a.e./acre
(21-day interval)
6.17
5.72
5.28
Direct Application to Water Uses
Rice
Direct water
application (Rice
model)
G & A
1 app @ 1.5 lb a.e./acre
1486
Aquatic Weed
Control5
Surface
application or
Direct water
application (Modeled
using aerobic aquatic
degradation rates)
G & A
1 app @ 10.8 lb a.e./acre foot
4000
3417
2610
85
-------
Table 3.4 Aqunlic KKCs lor 2.4-1) Acid/Ssill I scs in ('sililorniii
Masler l.ahel
PR/.M/I.WMS
Scenario
(first app dale)
Mclhod:
Application Kale
1.1
(fiji a.e./l.)
I se ( alexin 1
(inlcnal hclwccn applications)
Peak
21-daj
Wl-daj
subsurface
injection for
submersed
weeds
Aquatic Weed
Control5
Irrigation
ditchbank
application
Direct water
application (Modeled
using aerobic aquatic
degradation rates)
G & A
2 app @ 2.0 lb a.e./acre
(30-day interval)
740
632
483
Aquatic Weed
Control5
Surface
application for
floating and
emergent
aquatic weeds
Direct water
application (Modeled
using aerobic aquatic
degradation rates)
G & A
2 app @ 4.0 lb a.e./acre
(21-day interval)
1480
1264
966
1 Uses are derived from Master Label for Reregistration of 2,4-Dichlorophenoxyacetic Acid Uses - Supported by the
2,4-D Industry and IR-4.
2G = ground application. A = aerial application.
3The Master Label indicates a maximum single application rate of 1.0 lb a.e./100 gallons spray for filberts, SRRD
verified that this rate is equivalent to a maximum single application rate should of 0.5 lb a.e./acre, which represents a
conservative estimate.
4Because EFED does not currently have a PRZM/EXAMS scenario for CA Sugarcane, sugarcane uses were modeled
using the CA Sugar beet scenario as a surrogate.
5 EECs from one application were calculated even though multiple applications are permitted.
6 Although only IPE is labeled for citrus use, EFED is modeling exposure to acid as it is expected that most aquatic
exposure will be to the acid, not 2,4-D IPE.
86
-------
Tsihle 3.5 Peak KIX s lor 2.4-1) listers in Surl'siee Wnler Due l» Dril'l Only mid Dril'l+UunolT
IVoni All Applimhle PK5 Modeling Scenarios
Masler l.ahol I so
PK/M/IA .WIS
Scenario
tl'irsl app dale)
Method2
Application Kale
Peak r.r.c
(ill* a.o./l.)
(a logon1
tinlcnal between applications)'
Drill
l)ril'(+
Runoff
Orchard Uses
Citrus
CA citrus STD
A
1 app (cu. 0.1 lb a.c./acrc
0.28
0.28
G
0.055
0.055
Agricultural - Food Crop Uses
Field Corn, Popcorn
CA Corn OP
A
1 app @ 1.0 lb a.e./acre March 15,
1 app @ 0.5 lb a.e./acre April 29
1 app @ 1.5 lb a.e./acre August 15
(pre-harvest)
4.2
4.66
(15-Mar)
G
1 app @ 1.0 lb a.e./acre March 15,
1 app @ 0.5 lb a.e./acre April 29
1 app @ 1.5 lb a.e./acre August 15
(pre-harvest)
0.83
2.70
Sweet Corn
CA Corn OP
(15-Mar)
A
1 app @ 1 lb a.e./acre March 15; 1
app (i 0.5 lb a.e./acre April 29
2.8
3.11
G
1 app @ 1 lb a.e./acre on March 15;
and 1 app @ 0.5 lb a.e./acre on
April 29
0.55
1.80
Potatoes
CA Potato RLF
A
2 apps @ 0.07 lb a.e./acre
(10-day interval)
0.196
0.19
(1-Apr)
G
2 apps @ 0.07 lb a.e./acre
(10-day interval)
0.0385
0.039
Cereal Grains
CA Wheat RLF
A
1 post-emergence app @ 1.25 lb
a.e./acre and 1 pre-harvest app @
0.5 lb a.e./acre (90-day interval)
3.5
5.09
(10-Feb)
G
1 post-emergence app @ 1.25 lb
a.e./acre and 1 pre-harvest app @
0.5 lb a.e./acre (90-day interval)
0.69
3.32
Grain or Forage
Sorghum
CA Wheat RLF
A
1 post-emergence app @ 0.5 lb
a.e./acre
1.4
2.04
(10-Feb)
G
1 post-emergence app @ 0.5 lb
a.e./acre
0.28
1.33
Fallow land and
CA Row Crop RLF
A
2 apps @ 2 lb a.e./acre
(30-day interval)
5.6
5.5
Crop Stubble
(1-Aug)
G
2 apps @ 2 lb a.e./acre
(30-day interval)
1.1
1.1
Agricultural - Non-food Crop Uses
Established Grass
Pastures,
Rangeland,
Perennial Grassland
Not in Agricultural
Production
CA Rangeland Hay
RLF
(1-Mar)
G
2 apps @ 2 lb a.e./acre
(30-day interval)
1.1
1.27
Non-agricultural Uses
CA Right-of-Way
A
1 app @ 4 lb a.e./acre
11.2
11.13
Non-cropland
RLF
(20-Feb)
G
1 app @ 4 lb a.e./acre
2.2
6.37
87
-------
1 able 3.5 Peak I.I
K's for 2.4-1) listers in Surface Water Due lo Drift Only and Dril't+Uunoff
from All Applicable PK5 Modeling Scenarios
Master l.ahcl I sc
PU/.M/I-'.XAMS
Scenario
(I'irsl app dale)
Method2
Application Kale
Peak I'.r.C
in Si a.e./l.)
(intcnal between applications)'
Drill
l)ril(+
Runoff
Forestry,
CA Forestry RLF
(1-Mar)
A
1 app (i 4 lb a.e./acre
11.2
13.25
Tree and Brush
Control
G
1 app @ 4 lb a.e./acre
2.2
7.14
Ornamental Turf
CA Turf RLF
A
2 apps @ 1.5 lb a.e./acre
(21-day interval)
4.2
4.14
(1-Mar)
G
2 apps @ 1.5 lb a.e./acre
(21-day interval)
0.83
0.83
Grass Grown for
CA Turf RLF
A
2 apps @ 2 lb a.e./acre
(21-day interval)
5.6
5.51
Seed and Sod
(1-Mar)
G
2 apps @ 2 lb a.e./acre
(21-day interval)
1.1
1.11
1 Uses are derived from Master Label for Reregistration of 2,4-Dichlorophenoxyacetic Acid Uses -
2,4-D Industry and IR-4.
2G = ground application. A = aerial application.
3Modeled EECs reflect exposure due to a single application of the chemical.
Supported by the
3.2.6 Groundwater Modeling of 2,4-D Acid
Based on SCIGROW modeling, the 2,4-D concentration in ground water is estimated to
be 0.0311 jig a.e./L, The result is based on inputs of 6.2 days for aerobic soil metabolism
half-life, 13.23 for Koc, and a total annual application rate of 4 lb a.e./acre.
3.2.7 Existing Monitoring Data
A critical step in the process of characterizing Estimated Environmental Concentrations
is comparing the modeled estimates with available surface water monitoring data. Most
of this monitoring data is non-targeted {i.e., study was not specifically designed to
capture 2,4-D concentrations in high use areas). 2,4-D data from the USGS NAWQA
program (http://water.usgs. gov.nawqa) and data from the California Department of
Pesticide Regulation (CDPR) are included in this assessment. Typically, sampling
frequencies employed in monitoring studies are insufficient to document peak exposure
values. This, coupled with the fact that these data are not temporally or spatially
correlated with pesticide application times and/or areas, limits the utility of these data in
estimating exposure concentrations for risk assessment. These monitoring data are
characterized in terms of general statistics including number of samples, frequency of
detection, maximum concentration, and mean from all detections, where that level of
detail is available.
3.2.7.1 USGS NAWQA Surface Water Data
Surface water monitoring data from the United States Geological Survey (USGS)
NAWQA program was accessed in July 2008 and all data for the State of California were
downloaded. A total of 264 water samples were analyzed for 2,4-D. Of these samples, 55
88
-------
(20.8%) had positive detections of 2,4-D greater than or equal to 0.1 |ig/L; among these
detections, 3 were equal to or higher than 1 |ig/L. The maximum 2,4-D detection was
1.39 |ig/L in the Arcade Creek near Del Paso Heights in Sacramento County. The second
highest concentration was 1.2 |ig/L, which was detected in the salt slough at Highway
165 near Stevinson in Merced County. The third highest was 1 |ig/L, which was detected
in San Joaquin River near Patterson in Stanislaus County. Data are summarized by
county in Table 3.6. In summary, there was no clear pattern in 2,4-D detections from
different use sites because 2,4-D was detected in a number of different types of
watersheds (agricultural, urban, mixed and other) as classified by the USGS land use
information.
Table 3.6 Summary of 2.4-1) Detections from N AW QA Sampling Data in
California
Coiinly
.Number of
Number <0.10
Highest Concentration
samples
MS/I-
(MK/I.)
Alpine
4
4
El Dorado
4
4
Merced
68
64
1.2
Nevada
4
4
Orange
6
0
0.27 (other 5 <0.15)
Sacramento
62
42
1.39
San Bernardino
5
0
all reported <0.15
San Joaquin
31
29
0.2
Stanislaus
54
45
1
Sutter
2
2
Yolo
24
15
0.78
3.2.7.2 USGS NAWQA Groundwater Data
Groundwater monitoring data from the United States Geological Survey (USGS)
NAWQA program were accessed in July 2008, and all data for the state of California was
downloaded. A total of 210 water samples were analyzed for 2,4-D. Of these samples,
180 samples were identified as less than 0.035 |ig/L; the other 30 were reported with
measurements less than 0.15 |ig/L.
3.2.7.3 California Department of Pesticide Regulation (CDPR)
Data
Pesticide monitoring studies in surface water were primarily carried out by the
California Department of Pesticide Regulation (CDPR), Environmental Hazard
Assessment Program (EHAP), United States Geological Survey (USGS), and the Central
Valley Regional Water Quality Control Board. Data from these and other studies are
documented in EHAP's surface water database (SURF). Surface water monitoring data
for 2,4-D was accessed and extracted from the CDPR on June 28, 2008. A total of 437
samples were available. Of these samples, 2,4-D was detected in 2 samples with greater
than 2.0 |ig/L (2.78 |ig/L and 2.1 |ig/L); both were located in Yolo County. The other two
89
-------
detections that were greater than 1.0 |ig/L were 1.39 |ig/L (Sacramento County) and 1.2
|ig/L (Merced County). Approximately 5% of the samples (23) ranged between 0.1 -
0.78 |ig/L. Approximately 90% of samples (394) reported the value of 0.
3.2.7.4 Atmospheric Monitoring Data
Based on 2,4-D's low vapor pressure (1.47 x 10"7 mm Hg @ 25 °C ) and Henry's Law
8 0
Constant (1.02 x 10" atm-m3/mol @ 25 C), volatilization loss of 2,4-D from soil and
water systems is expected to be insignificant. Based on relatively low volatility and high
sensitivity to photolytic degradation, 2,4-D is not expected to continue long-range
transport. Considering the uses of 2,4-D in California, all 2,4-D formulations are
classified in terms of vapor pressure. Acid and salt forms are classed as "non-volatile"
salts. Ester formulations are classified as either "high-volatile" or "low-volatile." All
2,4-D forms are classified as toxic air contaminants (TAC) according to CDPR
(http://www.cdpr.ca.gov/docs/risk/priot.pdf). Two 2,4-D air monitoring studies were
funded by California Department of Food and Agriculture in 1980. The first study
showed that no positive 2,4-D air monitoring results were observed in a wide area of San
Joaquin Valley (Simpson et al., 1980). The second study also showed that no 2,4-D
dimethylamine salt or isobutyl ester was detected in any of the samples collected (Neher
et al., 1980).
3.2.8 Downstream Dilution Analysis
As previously stated (Section 2.7), for 2,4-D, both the initial area of concern and the action
area are considered to be the entire state of California. Due to the fact that the 2,4-D labels
allow for aquatic uses in multiple types of water bodies, multiple applications within a
specific watershed may occur within the same time frame. As a result, there is potentially no
input of "2.4-D clean" water to dilute existing concentrations of 2,4-D downstream because it
could be applied in the downstream waterbodies as well. Therefore, no credible watershed
dilution can be done. For that reason, a downstream dilution analysis was not conducted.
3.3 Terrestrial Animal Exposure Assessment
T-REX (Version 1.4.1) is used to calculate dietary and dose-based EECs of 2,4-D for
birds, mammals, and terrestrial invertebrates. T-REX simulates a 1-year time period.
For this assessment, spray and granular applications of 2,4-D are considered.
Terrestrial EEC modeling inputs for foliar application formulations of 2,4-D were
calculated by T-REX and summarized in Tables 3.7.a and 3.7.b, In addition to usage
input values (application rates, number of applications, and application intervals), T-REX
also utilizes a foliar dissipation half-life to estimate exposure. If chemical specific foliar
dissipation data are not available, EFED uses a default half-life of 35 days (Willis and
McDowell, 1987). Willis and McDowell (1987) did provide a foliar dissipation half-life
for 2,4-D of 8.8 days. In addition, several forest field dissipation studies submitted to the
Agency reported half-lives on foliage ranging from 33 to 42 days (MRIDs 439547-02,
439083-03 and 439271-01). Because study limitations created a great deal of uncertainty
in these half-lives (e.g., foliage only sampled from understory, some pre-treatment
90
-------
samples tested positive for 2,4-D, and concentrations were determined on a wet weight
basis), EFED utilized the 8.8-day half-life for terrestrial organism exposure estimation.
EFED included the aquatic application scenarios (rice and aquatic weed control) in the
terrestrial exposure assessment. Often the treated water bodies will be quite shallow,
making them accessible to terrestrial organisms. It is also likely that some 2,4-D will be
deposited off the target site and onto the land adjoining the treated water bodies.
For modeling purposes, exposures of the CRLF and AW to 2,4-D through contaminated
food items are estimated using the EECs for the small bird (20 g), which consumes small
insects. Dietary-based and dose-based exposures of potential prey of the CRLF and the
AW are assessed using the small mammal (15 g), which consumes short grass. In
addition, dietary-based and dose-based exposures of potential avian prey of the AW are
assessed using the small birds (20 g), which consumes short grass. Upper-bound Kenega
nomogram values reported by T-REX for these organism types are used for derivation of
EECs for the CRLF and the AW and their potential prey (Tables 3.7.a and 3.7.b), T-
REX is also used to calculate EECs for terrestrial insects exposed to 2,4-D. Dietary-
based EECs calculated by T-REX for small and large insects (units of a.e./g) are used to
bound an estimate of exposure to insects (Table 3.7.b), A sample output from T-REX is
available in Appendix J.
Exposure calculated as mg a.e./sq ft is provided for all granular applications (Table 3.8).
For granular applications, exposure is only estimated for a single application.
Table 3.7.a I pper-bound kenega Nomogram 1
Terrestrial-phase CUM'' and AW and its Prev
.IX s lor Dietary-and Dose-based Kxposures ol'tlie
o Liquid Applications of 2.4-1)
r.r.Cs lor CRI.r and \\V
r.r.Cs Tor Mammalian Prey'
(Indirect ell'ecls lo CRI.I-"
and AW )
Modeling
Scenario
Method1
Application Kale
Dielan-based
r.r.c mi"
a.c./kti-diel)
Dose-based
r.r.c
(niii a.e./kii-
Im)
Dielan-
based r.r.c
(niii a.e./kii-
dicl)
Dose-based
n:c
(niii a.e./kii-
Im)
Orchard Uses
Nut Orchards,
Pistachios
G
2 apps @ 2 lb a.e./acre
(30-day interval)
295
336
525
501
Filberts
G
4 apps @ 0.5 lb a.e./acre
(30-day interval)
75
85
132
126
Grapes (all)
G
1 app @ 1.36 lb a.e./acre
184
209
326
311
Blueberries
G
2 apps @ 1.4 lb a.e./acre
(30-day interval)
207
236
368
351
Stone and
Pome Fruits
G
2 apps @ 2 lb a.e./acre
(7 5-day interval)
271
308
481
459
Citrus
A/G
1 app (i 0.1 lb a.e./acre
14
15
24
23
Agricultural - Food Crop Uses
Field Corn,
Popcorn
A/G
1 app @ 1.0 lb a.e./acre
March 15,
203
231
360
344
91
-------
Table 3.7.si Ippcr-bound kcncgn Nomogram KIX s lor l)icl;irv-;iii(l Doso-hnsctl Kxposurcs of the
Tcm'slriul-phnsc CUM'' ;iihI AW sind its I'rcv lo Liquid Applications of 2.4-1)
r.r.Cs for CRI.r and \\V
r.r.Cs for Mammalian Prey'
(Indirccl cITecls (o ( KI.I-"
and AW )
Modeling
Scenario
Mclliod'
Applicalion Kale
Dielan-based
r.r.c mi"
a.e./kg-diel I
Dose-based
r.r.c
(nig a.e./kg-
b\\)
Dielan-
based i:r.c
(nig a.e./kg-
diel)
Dose-based
n:c
(nig a.e./kg-
b\\)
1 app @ 0.5 lb a.e./acre
April 29,
1 app @ 1.5 lb a.e./acre
August 15
1 app @ 1 lb a.e./acre
Sweet Corn
A/G
March 15,
1 app @ 0.5 lb a.e./acre
April 29
135
154
240
229
Potatoes
A/G
2 apps @ 0.07 lb a.e./acre
(10-day interval)
14
16
24
23
Sugarcane
A/G
2 apps @ 2 lb a.e./acre
(20-day interval)
326
371
579
552
Cereal Grains
A/G
1 post-emergence app @ 1.25
lb a.e./acre and 1 pre-harvest
app @ 0.5 lb a.e./acre
(90-day interval)
169
192
300
286
Grain or
Forage
Sorghum
A/G
1 post-emergence app @1.0
lb a.e./acre
135
154
240
229
Hops
A/G
3 apps @ 0.5 lb a.e./acre
(30-day interval)
74
85
132
126
Asparagus
A/G
2 apps @ 2 lb a.e./acre
(30-day interval)
295
336
525
501
Fallowland
and Crop
Stubble
A/G
2 apps @ 2 lb a.e./acre
(30-day interval)
295
336
525
501
Agricultural - Non-food Crop Uses
Established
Grass
Pastures,
Rangeland,
Perennial
Grassland Not
in Agricultural
Production
G
2 apps @ 2 lb a.e./acre
(30-day interval)
295
336
525
501
Non-agricultural Uses
Non-cropland
A/G
1 app @ 4 lb a.e./acre
540
615
960
915
Forestry
A/G
1 app @ 4 lb a.e./acre
540
615
960
915
Tree and
Brush Control
A/G
1 app @ 4 lb a.e./acre
540
615
960
915
Ornamental
Turf
A/G
2 apps @ 1.5 lb a.e./acre
(21-day interval)
241
275
429
409
Grass Grown
for Seed and
A/G
2 apps @ 2 lb a.e./acre
(21-day interval)
322
366
572
545
92
-------
Table 3.7.si I ppcr-hound kcncga Nomogram LLCs lor Dictary-and Dosc-hascd Lxposurcs ol'llic
Tcrrcslrial-pliasc CUM'' ;iihI AW and its I'rcv lo Liquid Applications of 2.4-1)
r.r.Cs lorCKI.Iand \\V
r.r.Cs Tor Mammalian Prey'
(Indirect ell'ecls (o CKI.I-"
and AW )
Modeling
Scenario
Method1
Application Kale
Dielan-hased
r.r.c mi"
a.e./kii-diel)
Dose-hased
r.r.c
(niii a.e./kii-
hw)
Dielan-
hased ll(
(in» a.e./kii-
diel)
Dose-hased
n:c
(in?* a.e./kii-
h\\)
Sod
Direct Application to Water Uses
Rice
A/G
1 app @ 1.5 lb a.e./acre
203
231
360
343
Aquatic Weed
Control
A/G
1 app @ 10.8 lb a.e./acre foot5
7290
8303
12960
12356
Aquatic Weed
Control
A/G
2 app @ 2 lb a.e./acre
(30-day interval)
295
336
525
501
Aquatic Weed
Control
A/G
2 app @ 4 lb a.e./acre
(21-day interval)
643
733
1144
1090
'G = ground application. A = aerial application.
2EECs based on small bird (20 g) which consumes small insects.
3EECs based on small mammal (15 g) which consumes short grass.
4These EECs also apply for terrestrial invertebrates (small insects).
5Label states apply 10.8 lb a.e./acre-foot. If water body is 5 ft deep, this equals an application rate of 54 lb a.e/.acre.
Table 3.7.b I
ppcr-hound kenega Nomogram
LLCs lor l)iclarv-and Dosc-hascd Lxposurcs ol'llic
Tcrrcslrial-pliasc (KIT
and AW and its I'rcv lo Liquid Applications of 2.4-1)
r.r.Cs for A\ ian Pre\
(1 iidireel r.lTccls lo AW r
r.r.Cs lor Terreslrial
ln\crlchralc Piv\ (Indirecl
r.lTccls lo CKI.I-' and AW)
Modeling
Scenario
Method1
Application Kale
Dielan-hased
r.r.c mi"
a.e./k*i-diel)
Dose-hased
n:c
(niii a.e./kji-
hw)
Small Insects
(in;i a.c./kji-
insecl)
Large
Inseels
(nig a.e./kg-
insecl)
Orchard Uses
Nut Orchards,
Pistachios
G
2 apps @ 2 lb a.e./acre
(30-day interval)
525
598
295
33
Filberts
G
4 apps @ 0.5 lb a.e./acre
(30-day interval)
132
151
75
8
Grapes (all)
G
1 app @ 1.36 lb a.e./acre
326
371
184
20
Blueberries
G
2 apps @ 1.4 lb a.e./acre
(30-day interval)
368
419
207
23
Stone and
Pome Fruits
G
2 apps @ 2 lb a.e./acre
(75-day interval)
481
548
271
30
Citrus
A/G
1 app (3> 0.1 lb a.e./acre
24
27
14
2
Agricultural - Food Crop Uses
Field Corn,
A/G
1 app @ 1.0 lb a.e./acre
360
410
203
23
93
-------
Table 3.7.h I ppcr-bound kcncga Nomogram KKCs lor Diclnrv-nnd Doso-bsisod Kxposurcs of 1 lie
Tcrrcslrinl-plinsc CUM'' mid AW and its I'rcv 1» Liquid Applications of 2.4-1)
r.r.Cs lor A\ inn Pro
(Indirect nice Is to AW r
r.r.Cs lor Tcrrcstrial
ln\crlchralc Prc\ (Indirect
r.lTecls to CKI.r and AW)
Modeling
Scenario
Method1
Application Kale
Diclan-bascd
r.r.c (m»
a.e./kg-diell
Dose-based
r.r.c
(m }i a.c./kg-
b\\)
Small Insects
tin}i a.e./kg-
insccl)
Large
Insects
(nig a.e./kg-
insccl)
Popcorn
March 15,
1 app @ 0.5 lb a.e./acre
April 29,
1 app @ 1.5 lb a.e./acre
August 15
1 app @ 1 lb a.e./acre
Sweet Corn
A/G
March 15,
1 app @ 0.5 lb a.e./acre
April 29
240
273
135
15
Potatoes
A/G
2 app @ 0.07 lb a.e./acre
(10-day interval)
24
28
14
2
Sugarcane
A/G
2 apps @ 2 lb a.e./acre
(20-day interval)
579
660
326
36
Cereal Grains
A/G
1 post-emergence app @
1.25 lb a.e./acre,
1 pre-harvest app @ 0.5
lb a.e./acre
(90-day interval)
300
342
169
19
Grain or
Forage
Sorghum
A/G
1 post-emergence app @
1.0 lb a.e./acre
240
273
135
15
Hops
A/G
3 apps @ 0.5 lb a.e./acre
(30-day interval)
132
151
75
8
Asparagus
A/G
2 apps @ 2 lb a.e./acre
(30-day interval)
525
598
295
33
Fallowland
and Crop
Stubble
A/G
2 apps @ 2 lb a.e./acre
(30-day interval)
525
598
295
33
Agricultural - Non-food Crop Uses
Established
Grass
Pastures,
Rangeland,
Perennial
Grassland Not
in Agricultural
Production
G
2 apps @ 2 lb a.e./acre
(30-day interval)
525
598
295
33
Non-agricultural Uses
Non-cropland
A/G
1 app @ 4 lb a.e./acre
960
1093
540
60
Forestry
A/G
1 app @ 4 lb a.e./acre
960
1093
540
60
Tree and
Brush Control
A/G
1 app @ 4 lb a.e./acre
960
1093
540
60
Ornamental
Turf
A/G
2 apps @ 1.5 lb a.e./acre
(21-day interval)
429
488
241
27
94
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Table 3.7.h I
ppcr-hoiind kenega Nomogram
LLCs lor Diclarv-and Dosc-hascd Lxposttrcs of 1 lie
Tcrrcslrial-phasc CUM'
and AW and its I'rcv lo Liquid Applications of 2.4-1)
r.r.Cs lor A\ ian Pro
(Indirecl I'.ITecls (o AW r
I'.r.Cs lor Terrestrial
ln\crlchralc I'rcv (Indirecl
Meets loCULI-and AW)
Modeling
Scenario
Method1
Application Kale
Diclan-hascd
r.r.c (m»
a.e./k*i-diel)
Dosc-hascd
r.r.c
Small Insccls
(in }i a.c./kji-
insecl)
Large
Insccls
(m }i a.e./kji-
(iii» a.c./kg-
h\\)
insecl)
Grass Grown
for Seed and
Sod
A/G
2 apps @ 2 lb a.e./acre
(21-day interval)
572
651
322
36
Direct Application to Water Uses
Rice
A/G
1 app @ 1.5 lb a.e./acre
360
410
203
23
Aquatic Weed
Control
A/G
1 app @ 10.8 lb a.e./acre
foot3
12960
14760
7290
810
Aquatic Weed
Control
A/G
2 app @ 2 lb a.e./acre
(30-day interval)
525
598
295
33
Aquatic Weed
Control
A/G
2 app @ 4 lb a.e./acre
(30-day interval)
1144
1303
643
72
'G = ground application. A = aerial application.
2EECs based on small bird (20 g) which consumes short grass.
3Label states apply 10.8 lb a.e./acre-foot. If water body is 5 ft deep, this equals an application rate of 54 lb a.e/.acre.
95
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Table 3.S KIX s lor Kxposures of Hie ( KLI- and AW and (heir Prev to (iranular
Applications of 2.4-1) ("round applications)
Scenario
Application Kale
i:i.(
(nig a.e./l'n
Agricultural Food Crop Uses
Field Corn, Popcorn
1 app @ 1.0 lb a.e./acre March
15, 1 app @ 0.5 lb a.e./acre
April 29, 1 app @ 1.5 lb
a.e./acre August 15
15.62
Sweet Corn
1 app @ 1 lb a.e./acre March 15;
1 app (i 0.5 lb a.e./acre April 29
10.41
Grain or Forage Sorghum
1 post-emergence app @ 1.0 lb
a.e./acre
10.41
Non-Agricultural Uses
Non-cropland
1 app @ 4 lb a.e./acre
41.65
Ornamental Turf
2 apps @ 1.5 lb a.e./acre
(21-day interval)
15.62
Grass Grown for Seed and
Sod
2 apps @ 2 lb a.e./acre
(21-day interval)
20.83
Direct Application to Water Uses
Aquatic Weed Control
1 app @ 10.8 lb a.e./acre foot
562.30
Aquatic Weed Control
2 app @ 2 lb a.e./acre
(30-day interval)
20.83
Aquatic Weed Control
2 app @ 4 lb a.e./acre
(21-day interval)
41.65
3.4 Terrestrial Plant Exposure Assessment
TerrPlant (Version 1.2.2) is used to calculate EECs for non-target plant species inhabiting
dry and semi-aquatic areas. Parameter values for application rate, drift assumption, and
incorporation depth are based upon the use and related application method. A runoff
value of 5% is utilized considering 2,4-D's solubility of 569 mg/L (>100 mg/L). For
aerial and ground application methods, drift is assumed to be 5% and 1%, respectively.
EECs relevant to terrestrial plants consider pesticide concentrations in drift and in runoff
(Table 3.9)
96
-------
Tsihlc 3.9 1 crrPhinl
Areas Kxposed l» 2.-
Inputs iiiul Resulting V.
-1) visi K ii no IT mid l)ri
IK's lor Phi ills Inhabiting l)rv ami Soni i-;i(| n;i 1 ic
'1 (single application onlv)
Modoli nii
Scenario
Melliod1
Application Kale
Drill
Value
Dn Area l.l.(
(lb a.e./acre)
Semi-a(|iialic
Area l.l.(
(lb a.e./acre)
Sprsij Drill l.l.(
(lb a.e./acre)
Orchard Uses
Nut
Orchards,
Pistachios
G
2 apps @ 2 lb a.e./acre
(30-day interval)
l
0.12
1.02
0.02
Filberts
G
4 apps @ 0.5 lb a.e./acre
(30-day interval)
l
0.03
0.25
0.005
Grapes (all)
G
1 app @ 1.36 lb a.e./acre
l
0.082
0.014
0.694
Blueberries
G
2 apps @ 1.4 lb a.e./acre
(30-day interval)
l
0.084
0.714
0.014
Stone and
Pome Fruits
G
2 apps @ 2 lb a.e./acre
(7 5-day interval)
l
0.12
0.02
1.02
Citrus
A/G
1 app @ 0.1 lb a.e./acre
l
5
0.006
0.01
0.051
0.055
0.001
0.005
Agricultural - Food Crop Uses
Field Corn,
Popcorn
A/G
1 app @ 1.0 lb a.e./acre
March 15,
1 app @ 0.5 lb a.e./acre
April 29,
1 app @ 1.5 lb a.e./acre
August 15
1
5
0.09
0.15
0.765
0.825
0.015
0.075
Sweet Corn
A/G
1 app @ 1 lb a.e./acre
March 15,
1 app @ 0.5 lb a.e./acre
April 29
1
5
0.06
0.10
0.51
0.55
0.01
0.05
Potatoes
A/G
2 apps @ 0.07 lb a.e./acre
(10-day interval)
1
5
0.004
0.007
0.036
0.039
0.0007
0.0035
Sugarcane
A/G
2 apps @ 2 lb a.e./acre
(20-day interval)
1
5
0.12
0.20
1.02
1.10
0.02
0.01
Cereal
Grains
A/G
1 post-emergence app @
1.25 lb a.e./acre,
1 pre-harvest app @ 0.5 lb
a.e./acre
(90-day interval)
1
5
0.075
0.125
0.638
0.688
0.013
0.063
Grain or
Forage
Sorghum
A/G
1 post-emergence app @
1.0 lb a.e./acre
1
5
0.06
0.10
0.51
0.55
0.01
0.05
Hops
A/G
3 apps @ 0.5 lb a.e./acre
(30-day interval)
1
5
0.03
0.03
0.25
0.25
0.005
0.05
Asparagus
A/G
2 apps @ 2 lb a.e./acre
(30-day interval)
1
5
0.12
0.20
1.02
1.10
0.02
0.01
Fallowland
and Crop
Stubble
A/G
2 apps @ 2 lb a.e./acre
(30-day interval)
1
5
0.12
0.20
1.02
1.10
0.02
0.01
97
-------
Tsihlc 3.9 1 crrPhinl
Areas Kxposed l» 2.-
Inputs iiiul Resulting V.
-1) visi K ii no IT mid l)ri
IK's lor Phi ills Inhabiting l)rv ami Soni i-;i(| n;i 1 ic
'1 (single application onlv)
Modoli nii
Scenario
Method'
Application Kale
Drift
Value
Dn Area l.l.(
(II) a.e./acre)
Scini-aqualic
Area l.l.(
(II) a.e./acre)
Sprsij Drill l.l.(
(II) a.e./acre)
Agricultural - Non-food Crop Uses
Established
Grass
Pastures,
Rangeland,
Perennial
Grassland
Not in
Agricultural
Production
G
2 apps @ 2 lb a.e./acre
(30-day interval)
1
0.12
1.02
0.02
Non-agricultural Uses
Non-
cropland
A/G
1 app @ 4 lb a.e./acre
1
5
0.24
0.40
2.04
2.20
0.04
0.20
Forestry
A/G
1 app @ 4 lb a.e./acre
1
5
0.24
0.40
2.04
2.20
0.04
0.20
Tree and
Brush
Control
A/G
1 app @ 4 lb a.e./acre
1
5
0.24
0.40
2.04
2.20
0.04
0.20
Ornamental
Turf
A/G
2 apps @ 1.5 lb a.e./acre
(21-day interval)
1
5
0.09
0.15
0.765
0.825
0.015
0.075
Grass
Grown for
Seed and
Sod
A/G
2 apps @ 2 lb a.e./acre
(21-day interval)
1
5
0.12
0.20
1.02
1.10
0.02
0.01
Direct Application to Water Uses
Rice
A/G
1 app @ 1.5 lb a.e./acre
1
5
0.09
0.15
0.765
0.825
0.015
0.075
Aquatic
Weed
Control
A/G
1 app @ 10.8 lb a.e./acre
foot3
1
5
3.24
5.40
27.54
29.70
0.54
2.70
Aquatic
Weed
Control
A/G
1 app @ 2 lb a.e./acre
1
5
0.12
0.20
1.02
1.10
0.02
0.01
Aquatic
Weed
Control
A/G
1 app @ 4 lb a.e./acre
1
5
0.24
0.40
2.04
2.20
0.04
0.20
'G = ground application. A = aerial application.
2EECs calculated based on a single application. If crop labeled for multiple applications within a year, the highest single
rate was used.
3Label states apply 10.8 lb a.e./acre-foot. If water body is 5 ft deep, this equals an application rate of 54 lb a.e/.acre.
98
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4. Effects Assessment
This assessment evaluates the potential for 2,4-D to directly or indirectly affect the CRLF
and AW or modify their designated critical habitat. As previously discussed in Section
2.7, assessment endpoints for the effects determination for each assessed species include
direct toxic effects on the survival, reproduction, and growth, as well as indirect effects,
such as reduction of the prey base or modification of its habitat. In addition, potential
modification of critical habitat is assessed by evaluating effects to the PCEs, which are
components of the critical habitat areas that provide essential life cycle needs of each
assessed species. Direct effects to the aquatic-phase CRLF are based on toxicity
information for freshwater fish (or amphibian data if appropriate), while terrestrial-phase
amphibian effects (terrestrial-phase CRLF) and reptiles (AW) are based on avian toxicity
data, given that birds are generally used as a surrogate for terrestrial-phase amphibians
and reptiles.
As described in the Agency's Overview Document (U.S. EPA, 2004), the most sensitive
endpoint for each taxon is used for risk estimation. For this assessment, evaluated taxa
include freshwater fish (used as a surrogate for aquatic-phase amphibians), freshwater
invertebrates, aquatic plants, birds (used as a surrogate for terrestrial-phase amphibians
and reptiles), mammals, terrestrial invertebrates, and terrestrial plants. Acute (short-term)
and chronic (long-term) toxicity information is characterized based on registrant-
submitted studies and a comprehensive review of the open literature on 2,4-D.
Toxicity endpoints are established based on data generated from guideline studies
submitted by the registrant and from open literature studies that meet the criteria for
inclusion into the ECOTOX database maintained by EPA/Office of Research and
Development (ORD) (U.S. EPA, 2004). Open literature data presented in this assessment
were obtained from the 2,4-D RED and the ECOTOX database, which was searched on
June 30, 2008. In order to be included in the ECOTOX database, papers must meet the
following minimum criteria:
(1) the toxic effects are related to single chemical exposure;
(2) the toxic effects are on an aquatic or terrestrial plant or animal species;
(3) there is a biological effect on live, whole organisms;
(4) a concurrent environmental chemical concentration/dose or application
rate is reported; and
(5) there is an explicit duration of exposure.
Data that pass the ECOTOX screen are evaluated along with the registrant-submitted data
and may be incorporated qualitatively or quantitatively into this endangered species
assessment. In general, effects data in the open literature that are more conservative than
the registrant-submitted data are considered. The degree to which open literature data are
quantitatively or qualitatively characterized for the effects determination is dependent on
whether the information is relevant to the assessment endpoints (i.e., survival,
reproduction, and growth) identified in Section 2.8. For example, endpoints such as
behavior modifications are likely to be qualitatively evaluated, because quantitative
99
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relationships between modifications and reduction in species survival, reproduction,
and/or growth are not available. Although the effects determination relies on endpoints
that are relevant to the assessment endpoints of survival, growth, or reproduction, it is
important to note that the full suite of sublethal endpoints potentially available in the
effects literature (regardless of their significance to the assessment endpoints) are
considered to define the action area for 2,4-D.
Citations of all open literature not considered as part of this assessment because they
were either rejected by the ECOTOX screen or accepted by ECOTOX but not used (e.g.,
the endpoint is less sensitive) are included in Appendix G. Appendix G also includes a
rationale for rejection of those studies that did not pass the ECOTOX screen and those
that were not evaluated as part of this endangered species risk assessment.
A detailed spreadsheet of the available ECOTOX open literature data, including the full
suite of lethal and sublethal endpoints is presented in Appendix G. Reviews of several
of the ECOTOX and open literature studies are also included in Appendix G.
In addition to registrant-submitted and open literature toxicity information, other sources
of information, including use of the acute probit dose response relationship to establish
the probability of an individual effect and reviews of the Ecological Incident Information
System (EIIS), are reviewed to further refine the characterization of potential ecological
effects associated with exposure to 2,4-D. A summary of the available aquatic and
terrestrial ecotoxicity information, use of the probit dose response relationship, and the
incident information for 2,4-D are provided in Section 4.
Several degradates have been reported for 2,4-D but only a few have been identified and
quantified. The Agency does not have concerns for any degradates of 2,4-D relative to
human health issues as the tolerance expression is only expressed in terms of the 2,4-D
parent based on the determination of the Metabolite Assessment Review Committee
(MARC) Health Effects Division (HED) of OPP. There is no evidence that any 2,4-D
degradates are of toxicological concern, and none of them (>10.0%) is found in a
significant amount; therefore, this assessment is based on parent 2,4-D (acid, salts, and
esters) only. Although ECOTOX data indicates the degradate 2,4-dichlorophenol (2,4-
DCP) is more toxic than the parent for freshwater fish, freshwater invertebrates, and
earthworms, the degradation of the parent only results in 3.5% available 2,4-DCP, which
would not result in toxicity concerns for direct or indirect effects to the CRLF or AW.
2,4-D has registered products that contain multiple active ingredients. Analysis of the
available open literature and acute oral mammalian LD50 data for multiple active
ingredient products relative to the single active ingredient is provided in Appendix A.
Based on a review of the available studies on 2,4-D mixtures in ECOTOX, it appears that
the toxicity values presented in the mixture papers are no more sensitive than the toxicity
of the single active ingredient, 2,4-D. The results of this analysis show that an
assessment based on the toxicity of the single active ingredient of 2,4-D is appropriate.
A recent paper by Relyea (2008, see review in Appendix G) evaluated the effects of
several pesticides alone and in combination on mesocosms containing aquatic
100
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communities consisting of zooplankton, phytoplankton, periphyton and larval amphibians
(gray tree frogs, Hyla versicolor and leopard frogs, Ranapipiens). Each insecticide
(malathion, carbaryl, chlorpyrifos, diazinon and endosulfan) and each herbicide
(glyphosate, atrazine, acetochlor, metolachlor and 2,4-D acid) was evaluated singly as
well as (a) all insecticides together, (b) all herbicides together, and (c) all insecticides and
herbicides together. 2,4-D alone and the mixture of all herbicides did not appear to have
any effects on the survival and metamorphosis of amphibian populations. However, there
was a slight reduction in phytoplankton population (that effect was also seen in the
acetochlor trial). The mixture of all insecticides and the mixture of all herbicides and
insecticides caused a 99% reduction in leopard frogs and no reduction in gray tree frogs;
because of this, gray tree frogs grew twice as large due to lack of competition.
4.1 Dioxin Contaminant Toxicity to Terrestrial Organisms
A key chemical intermediate in the manufacture of 2,4-D is 2,4-dichlorophenol (2,4-
DCP), and the purity of this intermediate has a strong correlation to the purity of 2,4-D
acid produced from it. In the manufacture of 2,4-DCP, multiple positions around the
phenyl ring structure may be chlorinated. The desired positions for chlorination are
carbons two and four of the phenyl ring, but the reaction may yield small quantities of
compounds chlorinated at different positions. Certain combinations of these chlorinated
structures may form precursors to the dioxin 2,3,7,8-TCDD.
According to 2,4-D registrants, since the 1990's, the manufacturing processes for 2,4-D
and its chemical intermediate, dichlorophenol, have been modified, and those
modifications decrease the chance that TCDD and PCDD are formed during the
manufacturing process. Manufacture of the 2,4-DCP intermediate has been optimized by
controlling processing conditions necessary to drive the chlorination reaction to the
preferred two and four carbon positions, thereby limiting the formation of impurities that
can lead to dioxin formation. Controlled temperature and residence time during the
chlorination reaction, programmed addition of the chlorinating agent, and efficient
agitation in the reaction vessel are processing factors that contribute to the purity of 2,4-
DCP. Additionally, distillation of 2,4-DCP is a technique that may be employed post-
chlorination to increase purity. Moreover, quality control sampling and analytical
procedures are also utilized to verify product quality at various steps of the 2,4-DCP
process. Results of testing of 2,4-DCP, performed in response to the Toxic Substances
Control Act (TSCA) Dioxin/Furan Test Rule, showed no detectable concentrations of
2,3,7,8-substituted tetra- through hepta-CDD/CDFs.
In the manufacture of 2,4-D acid per se, there are additional process conditions and
procedures that must be controlled to maximize yield and purity. Details regarding these
measures are dependent on specific manufacturing methodologies and, as such, are
protected under FIFRA Section 10 as Confidential Business Information.
The Agency's most recent evaluations of anticipated dioxin and furan residues resulting
from 2,4-D applications are based on the concentrations of dioxins and furans present in
technical grade 2,4-D as determined by review of analytical data submitted in response
101
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to the 1987 DCI. In those evaluations, completed in the early 1990's, the ratios of
individual chlorodibenzo-p-dioxin (CDD; dioxin) or chlorodibenzo-p-furan (CDF;
furan) contaminant concentrations to 2,4-D acid concentrations were calculated, and
those ratios were used with 2,4-D tolerance expressions to calculate an anticipated
residue in eggs, fruits, grains, kidney (hogs), meat (hogs), milk, nuts, poultry, and
sugarcane for each detected dioxin or furan(SRRD RED, June 2005).
In addition to the above analysis for tolerance expressions, EFED completed a revised
ecological risk assessment (May 31, 2005) to assess reproductive effects to piscivorous
birds and mammals from exposure to PCDD and PCDF in technical 2,4-D and 2,4-D
ester herbicides (see excerpts in Appendix E).
For each technical 2,4-D formulation for which the Agency received data, calculation of
an anticipated dietary exposure was based on a worst-case scenario in which the highest
anticipated residue was used, and an assumption was made that 100% of the diet
consisted of the food item with the highest anticipated residue. Based on the
confidential EFED risk assessment (May 31, 2005), there was no toxicity concerns for
reproductive effects to piscivorous birds and mammals. The risk quotients were orders
of magnitude below the LOC. The high runoff PRZM/EXAMS scenario (NC apple) was
used to assess terrestrial runoff exposure. Because CA sites have lower runoff amounts
than the NC sites, it is reasonable to assume that there will be no effect in the CRLF and
AW assessment. Therefore, based on the calculation of dietary exposures using the
worst-case scenarios, cancer, non-cancer, and reproductive (in birds and mammals) risks
based on dietary exposure to dioxins and furans as contaminants of 2,4-D were
considered to be of no toxicological concern.
4.2 Toxicity of 2,4-D to Aquatic Organisms
Table 4.1.a and 4.1.b summarize the most sensitive aquatic toxicity endpoints, based on
an evaluation of both the submitted studies and the open literature, as previously
discussed. A brief summary of submitted and open literature data considered relevant to
this ecological risk assessment for the CRLF is presented below. Additional information
is provided in Attachment 3. Because the AW is a terrestrial organism given its
designated critical habitat as well as its prey base, the aquatic assessment does not
include direct or indirect effects to the AW.
Toxicity to fish and aquatic invertebrates is categorized using the system shown in Table
4.2 (U.S. EPA, 2004). Toxicity categories for aquatic plants have not been defined.
102
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Tsihlc 4.1 .;i Krcshwsilcr Aqusilic Toxicity Profile lor 2.4-1) Acid siml Ssills (l).MA. I I PA. IPA.
I)i: \. Nsi)
Assessment l.nripoinl
Species
To\icil> Yiiluc I sed in
Risk Assessment
MRU)
(Author & Diiie)
Si;iius/( onimcnl
Acute Direct Toxicity to
Aquatic-phase CRLF
Common carp
(Cyprinus
carpio)
LC50 = 24.15 mg a.e./L
E006387
(Vardia and
Durve, 1981)
Use quantitatively
Chronic Direct Toxicity to
Aquatic-phase CRLF
Fathead Minnow
(Pimephales
promelas)
NOAEC = 14.2 mg
a.e./L
417677-01
(Dill et al., 1990)
Acceptable
Indirect Toxicity to Aquatic-
phase CRLF via Acute
Toxicity to Freshwater
Invertebrates (i.e., prey items)
Water Flea
(Daphnia magna)
EC50= 25 mg a.e./L
411583-01
(Alexander et al.,
1983)
Acceptable
Indirect Toxicity to Aquatic-
phase CRLF via Chronic
Toxicity to Freshwater
Invertebrates (i.e., prey items)
Water flea
(Daphnia magna)
NOAEC = 16.05 mg
a.e./L
420183-03
(Holmes et al.,
1991)
Acceptable
Indirect Toxicity to Aquatic-
phase CRLF via Toxicity to
Non-vascular Aquatic Plants
Freshwater
Diatom
(Navicula
pelliculosa)
EC50 = 3.88 mg a.e./L
415059-03
(Hughes, 1990)
Acceptable
Indirect Toxicity to Aquatic-
phase CRLF via Toxicity to
Vascular Aquatic Plants
Water Milfoil
(Myriophyllum
sibiricum)
EC50 = 0.0131 mg
a.e./L
E74985
(Roshon, 1997)
Use quantitatively
Tsihlc 4.1.1) Krcshwsilcr Aqusilic I'oxicilv Profile lor 2.4-1) Kslcrs (2-KIIK. liKK. IPK)
Assessment r.nripoinr'
Species
Toxicity Yiiluc I sed in
Risk Asscssmcnl
MRU)
(Author & Diilc)
Si;iius/( onimcnl
Acute Direct Toxicity to
Aquatic-Phase CRLF
Bluegill Sunfish
(Lepomis
macrochirus)
LC50 = 0.26 mg a.e./L
439307-01,
439103-01
(Drottar et al.,
1996)
Acceptable
Chronic Direct Toxicity to
Aquatic-Phase CRLF
NA
NA
NA
NA
Indirect Toxicity to Aquatic-
Phase CRLF via Acute
Toxicity to Freshwater
Invertebrates (i.e., prey items)
Water Flea
(Daphnia
magna)
LC50 = 2.2 mg a.e./L
439306-01
(Drottar et al.,
1996)
Acceptable
Indirect Toxicity to Aquatic-
Phase CRLF via Chronic
Toxicity to Freshwater
Invertebrates (i.e., prey items)
NA
NA
NA
NA
103
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Table 4.1.b Kreshwater Aquatic Toxicity Profile lor 2.4-1) listers (2-KIIK. IJKK. IPK)
Indirect Toxicity to Aquatic-
Phase CRLF via Toxicity to
Non-vascular Aquatic Plants
Marine Diatom
(Skeletonema
costatum)
EC50 = 0.066 mg a.e./L
417352-04
(Hughes, 1990)
Acceptable
Indirect Toxicity to Aquatic-
Phase CRLF via Toxicity to
Vascular Aquatic Plants
Duckweed
(Lemna gibba)
EC50 = 0.33 mg a.e./L
417352-03
(Hughes, 1990)
Acceptable
aAlthough chronic aquatic toxicity data for esters were reviewed, most sensitive endpoints are not included in this
toxicity profile because chronic risks of esters were not estimated because the hydrolysis soil slurry data indicate that
dissipation in a non-sterile water body will occur at all PHs; therefore, long-term exposures are unlikely.
Table 4.2 Categories of Acute Toxicity lor Aquatic Animals
1 .C ippni)
Tu\icil> ( ;ik'iion
<0.1
Very highly toxic
>0.1-1
Highly toxic
>1-10
Moderately toxic
> 10 - 100
Slightly toxic
> 100
Practically non-toxic
4.2.1 Toxicity to Freshwater Fish and Aquatic-phase Amphibians
Although several registrant-submitted and ECOTOX studies evaluating the acute toxicity
to aquatic-phase amphibians were reviewed, EFED determined that the use of freshwater
fish data is preferable to the use of aquatic-phase amphibian data because it is unknown
where the CRLF would fall on a species sensitivity distribution. Because amphibian data
is not required from the registrant, it is EFED's standard approach to use freshwater fish
as a surrogate for aquatic-phase amphibians. In addition, because acute amphibian data
were less sensitive than acute freshwater fish data, the use of freshwater fish as a
surrogate provides a more conservative estimation of risk to the aquatic-phase CRLF.
Chronic aquatic-phase amphibian toxicity data were not available.
Freshwater fish toxicity data were also used to assess potential indirect effects of 2,4-D to
the CRLF. Effects to freshwater fish resulting from exposure to 2,4-D have the potential
to indirectly affect the CRLF via reduction in available food, as over 50% of the prey
mass of the CRLF may consist of vertebrates such as mice, frogs, and fish (Hayes and
Tennant, 1985).
4.2.1.1 Freshwater Fish: Acute Exposure (Mortality) Studies
Acute toxicity to freshwater fish can be summarized as practically non-toxic for the acid
and salts and highly toxic for the esters. Definitive LC50 values for the acid and salts
range from 101 to 2244 mg a.e./L; non-definitive LC50 values range from >81.6 to >830.0
mg a.e./L. The registrant-submitted study that reported the most sensitive toxicity value
was for 2,4-D DEA salt with an LC50 of 101 mg a.e./L (MRID 0073-091-01); however, a
more sensitive endpoint was found in the open literature.
104
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The ester LC50 values range from 0.26 to 14.5 mg a.e./L. The most sensitive toxicity
value was reported for two IPE studies (one with technical, and one with an end-use
product), both with LC50 values of 0.26 mg a.e./L (MRID 439307-01, 439103-01). This
value will be used to quantitatively estimate risks to the aquatic-phase CRLF.
4.2.1.2 Freshwater Fish: Chronic Exposure (Growth/Reproduction)
Studies
Chronic toxicity, based on larval survival and fish length from the early life stage studies,
NOAECs range from 14.2 to 63.4 mg a.e./L for acids and salts. For risk estimation, the
NOAEC of 14.2 mg a.e./L for DMA salt will be used (MRID 417677-01, most sensitive
endpoint of length).
One full life cycle study was submitted to the Agency for 2,4-D EHE. This study resulted
in a NOAEC of 0.0792 mg a.e./L, with the most sensitive endpoint of larval survival
(MRID 417373-05). Although there was a registrant-submitted study that evaluated the
chronic toxicity of esters to freshwater fish, this study will not be used in the assessment
as chronic risks of esters were not evaluated due to the unlikelihood of long-term
exposures (see Environmental Fate Strategy in Section 2.4.1),
4.2.1.3 Freshwater Fish: Open Literature Data
For acids and salts, acute LC50/EC50 values ranged between 0.014 and 2884 mg a.e./L.
However, some of these studies with low toxicity values were not scientifically sound or
did not provide sufficient data to be used quantitatively in this risk assessment. A study
that evaluated the effects of 2,4-D acid on the common carp resulted in a 96-hr LC50 of
24.15 mg a.e./L (E006387), which was more sensitive than the lowest reported value
from registrant-submitted data; therefore, it will be used for quantitative acute risk
estimation. One ECOTOX study (E000563) evaluated the chronic effects of 2,4-D
potassium salt on several species of freshwater fish; however, insufficient data were
available to determine a NOAEC.
For esters, acute LC50 values ranged from 0.302 to 8.8 mg a.e./L. None of these studies
reported values that were more sensitive than the values reported in the registrant-
submitted study. There were two studies that evaluated the chronic effects of esters
(NOAECs ranged from 0.04 to 0.075 mg a.e./L); however, these studies will not be used
in this risk assessment since chronic risks of esters were not evaluated due to the
unlikelihood of long-term exposures (see Environmental Fate Strategy in Section 1).
4.2.1.4 Aquatic-phase Amphibian: Acute Studies
Two studies evaluating the effects of the acid and DMA on leopard frog tadpoles were
submitted by the registrant and resulted in LCso's ranging from 278 to 359 mg a.e./L. For
both BEE and EHE, registrant-submitted studies resulted in LC50 values of 0.505 mg
a.e./L.
105
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ECOTOX and open literature studies evaluating acute effects to aquatic-phase
amphibians resulted in definitive endpoints (either LC50 or EC50) ranging between 181
and 1962 mg a.e./L and a non-definitive endpoint of >38.9 mg a.e./L for acid and salts.
No open literature studies that were conducted using an ester resulted in a lower toxicity
than the registrant-submitted studies.
4.2.2 Toxicity to Freshwater Invertebrates
4.2.2.1 Freshwater Invertebrates: Acute Exposure Studies
Several registrant-submitted studies evaluating the acute effects of acid and salts on
freshwater invertebrates provided an LC50 range of 25 to 642.8 mg a.e./L. For the
purposes of risk estimation, the acid LC50 value of 25 mg a.e./L will be used (MRID
411583-01).
For esters, registrant-submitted studies reported a range of LC50 values from 2.2 to 11.88
mg a.e./L. For risk estimation, the IPE LC50 value of 2.2 mg a.e./L will be used (MRID
439306-01).
4.2.2.2 Freshwater Invertebrates: Chronic Exposure Studies
Two registrant-submitted studies were submitted resulting in aNOAEC range of 16.05 to
79 mg a.e./L for chronic effects of acid and salts. A third study did not provide a
NOAEC; however, an LC50 = 75.7 mg a.e./L was determined. For the purposes of risk
estimation, the DEA salt NOAEC of 16.05 mg a.e./L will be used (MRID 420183-03).
One chronic study was submitted by the registrant for esters (resulting in a NOAEC of
0.20 mg a.e./L for BEE; however, this study will not be use for chronic risk estimation as
esters were not evaluated due to the unlikelihood of long-term exposures (see
Environmental Fate Strategy in Section 2.4.1),
4.2.2.3 Freshwater Invertebrates: Open Literature Data
ECOTOX and open literature data for acute effects of acid and salts on freshwater
invertebrates provided an LC50/EC50 range of 0.1245 and 436.5 mg a.e./L. Although some
toxicity values were more sensitive than registrant-submitted values, those studies were
not scientifically sound or did not provide sufficient data to be used quantitatively in this
risk assessment.
Definitive LCso/EC50 values for esters ranged between 0.3036 and 4.4 mg a.e./L; one
non-definitive LC50 value was > 69 mg a.e./L. None of these endpoints will be used for
quantitative risk estimation. Although some toxicity values were more sensitive than
registrant-submitted values, those studies were not scientifically sound or did not provide
sufficient data to be used quantitatively in this risk assessment.
No chronic studies were reviewed in ECOTOX or open literature.
106
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4.2.3 Toxicity to Aquatic Plants
Laboratory and field studies are the two types of studies used to evaluate the potential of
2,4-D to affect vascular and non-vascular aquatic plants. No field studies were available
that evaluated the risks to aquatic plants at the time of this assessment. For non-vascular
plant laboratory data, the toxicity values used for risk estimation can be observed from
either freshwater or estuarine/marine species since guideline studies do not sufficiently
explore the relative sensitivity of algae with regards to freshwater or estuarine/marine
environment.
4.2.3.1 Aquatic Plants: Laboratory Data
Vascular Plants
Registrant-submitted Tier II studies reported effects of acid and salts to vascular plants
provided an EC50 range of 0.2992 to 1.28 mg a.e./L. However, a more sensitive toxicity
value was reported in open literature study; none of the registrant-submitted toxicity
values will be used for estimation of risks of acids and salts to aquatic plants.
Two registrant-submitted Tier II studies reported an EC50 range of 0.33 to 0.3974 mg
a.e./L for toxicity of esters to vascular plants. The 2-EHE EC50 of 0.33 mg a.e./L will be
used for the purposes of risk estimation of esters to vascular plants (MRID 417352-03).
ECOTOX and open literature data for effects of acids and salts on aquatic vascular plants
provided an EC50 range of 0.0131 and 0.334 mg a.e./L. Because the study providing the
EC50 = 0.0131 mg a.e./L toxicity value was more sensitive than the value reported in the
registrant-submitted study, this value will be used to quantitatively estimate the risks to
aquatic vascular plants (E74985).
No studies were found in ECOTOX or open literature that evaluated the effects of esters
on aquatic vascular plants.
Non-vascular Plants
For non-vascular aquatic plants, registrant-submitted Tier II studies reported effects of
acid and salts with an EC50 range of 3.88 to 156.5 mg a.e./L. For risk estimation, the
DMA salt EC50 of 3.88 mg a.e./L will be used (MRID 415059-03).
For ester toxicity to non-vascular aquatic plants, registrant-submitted Tier II studies
reported an EC50 range from 0.066 to 19.8 mg a.e./L. The 2-EHE EC50 of 0.066 mg a.e./L
will be used for the purposes of risk estimation (MRID 417352-04).
In addition to the Tier II studies, several Tier I studies were submitted and reviewed for
the acid and IPE. Since the Tier II studies provided more detailed information about the
107
-------
toxicity of 2,4-D and most provided more sensitive toxicity values, they will be used in
the risk assessment.
For effects of acids and salts on aquatic non-vascular plants, there were two studies in
ECOTOX, but neither of these studies provided a definitive toxicity value that was less
than the value reported in the registrant-submitted study. No studies were found in
ECOTOX or open literature that evaluated the effects of esters on aquatic non-vascular
plants.
4.3 Toxicity of 2,4-D to Terrestrial Organisms
Table 4.3 summarizes the most sensitive terrestrial toxicity endpoints, based on an
evaluation of both the submitted studies and the open literature. A brief summary of
submitted and open literature data considered relevant to this ecological risk assessment
is presented below. All registrant submitted studies are summarized in Appendix F.
Acute toxicity to terrestrial animals is categorized using the classification system shown
in Table 4.4 (U.S. EPA, 2004). Toxicity categories for terrestrial plants have not been
defined.
Table 4.3 Terrestrial Toxicity Profile lor 2.4-1)
I'lndpoiiii
Aculc/
Chronic
Species
Toxicity
Value I scd
in Risk
AsscssmciK
MRU)
( Author & Diilc)
( <11111110111
Birds
(surrogate
for
terrestrial-
phase
amphibians
and reptiles)
A(gavage)
Bobwhite quail
LD50 = 298
mg a.e./kg-bw
442757-01
(Beavers, 1985)
Moderately toxic
Acceptable,
conducted using IPA
A(dietary)
Bobwhite quail
Mallard duck
LC50 > 3035
mg a.e./kg-
diet
416444-02
(Driscoll et al.,
1990)
416444-03
(Driscoll et al.,
1990)
Slightly toxic
Acceptable, both
conducted using
TIPA
C
Bobwhite quail
NOAEC =962
LOAEC >962
415861-01
(Culotta, 1989)
No significant
effects.
Acceptable,
conducted using acid
Mammals
A
Laboratory rat
LD50 = 441
414135-01
Moderately toxic,
Acceptable,
conducted using
TIPA
C
Laboratory rat
NOAEL =
5mg a.e./kg-
bw/day
00150557
00163996
Decreased female
body wt gain(Fl) and
male renal tubule
alteration (F0 and
Fl); decreased pup
weights
108
-------
Table 4.3 Terrestrial Toxicity Profile lor 2.4-1)
I'lndpoiiii
Aculc/
Chronic
Species
Toxicity
Yiiluc I scd
in Risk
Assessment
MRU)
(Author & Diile)
( ommciil
Acceptable,
conducted using acid
Terrestrial
invertebrates
A
Honey bee,
contact
LD50 >66 (ig
a.e./bee
445173-01
Acceptable,
conducted using
EHE
Terrestrial
plants
N/A
Seedlins
Emersence
Monocots
EC25 = 0.097
lb a.e./acre
471060-01
(Porch et al.,
2006)
Onion, dry weight
Acceptable,
conducted using
DMA TEP
N/A
Seedlins
Emersence
Dicots
EC25= 0.012
lb a.e./acre
471060-03
(Porch et al.,
2006)
Tomato, dry weight
Acceptable,
conducted using
EHE TEP
N/A
Vesetative
Vigor
Monocots
EC25 = 0.088
lb a.e./acre
471060-04
(Porch et al.,
2006)
Onion, dry weight
Acceptable,
conducted using
EHE TEP
N/A
Vesetative
Vigor
Dicots
EC25 = 0.0021
lb a.e./acre
471060-04
(Porch et al.,
2006)
Lettuce, dry weight
Acceptable,
conducted using
EHE TEP
N/A: not applicable
Table 4.4 Categories of Acute I'oxicilv lor Terrestrial Organisms
Ciilciiorics of Aculc Toxicilj lor Birds ;iihI M;imm;ils
Toxicity Ciilciion
Oiiil 1.1),,,
l)icl;in l.(
Very highly toxic
< 10 mg/kg
< 50 ppm
Highly toxic
10 - 50 mg/kg
50 - 500 ppm
Moderately toxic
51 -500 mg/kg
501 - 1000 ppm
Slightly toxic
501 - 2000 mg/kg
1001 - 5000 ppm
Practically non-toxic
> 2000 mg/kg
> 5000 ppm
Ciilciiorics of Aculc To\icil\ lor Non-Tiiificl Insccls
l'o\icil\ Ciilc^on
I.C
lllglll^ loxic
2 ^g. bcc
Moderately toxic
2-11 ng/bee
Practically nontoxic
>11 ng/bee
109
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4.3.1 Toxicity to Birds
As specified in the Overview Document, the Agency uses birds as a surrogate for reptiles
and terrestrial-phase amphibians when toxicity data for each specific taxon are not
available (U.S. EPA, 2004). No reptile or terrestrial-phase amphibian data were available
for 2,4-D.
4.3.1.1 Birds: Acute Exposure (Mortality) Studies
Seven bobwhite quail gavage toxicity studies for various forms of 2,4-D were submitted
to the Agency. Five had definitive LD50s, ranging from 298 to 1578 mg a.e./kg-bw, and
two had non-definitive LD50s, which were >219 and >1380 mg a.e./kg-bw. Five mallard
duck gavage toxicity studies were submitted to the Agency. All resulted in non-definitive
LD50s ranging from >314 to >5620 mg a.e./kg-bw. The LD50 of 298 mg a.e./kg-bw will
be used for risk estimation (MRID 442757-01, conducted with IP A).
Nine bobwhite quail dietary toxicity studies for various forms of 2,4-D were submitted to
the Agency. All had non-definitive LC50s, ranging from >3035 to >8300 mg a.e./kg-diet.
Eight mallard duck dietary toxicity studies were submitted to the Agency. All resulted in
non-definitive LC50s ranging from >3035 to >5620 mg a.e./kg-diet. The lowest LC50s,
both obtained from studies conducted with TIP A, will be used for risk estimation
(MRIDs 416444-02 and 416444-03, no mortalities or overt signs of toxicity at any test
concentration).
4.3.1.2 Birds: Chronic Exposure (Growth, Reproduction) Studies
One reproductive study (bobwhite quail) was submitted to the Agency using 2,4-D acid.
This study resulted in a NOAEC of 926 mg a.e./kg-diet, the highest concentration tested.
No significant effects were noted at any concentration. This will be used for chronic risk
estimation for all forms of 2,4-D.
4.3.1.3 Birds: Open Literature Data
None of the ECOTOX or open literature data provided acute toxicity information that
was more sensitive than those values reported in the registrant-submitted data.
Several avian reproductive studies were available in ECOTOX. Although some toxicity
values were more sensitive than registrant-submitted values, those studies were not
scientifically sound or did not provide sufficient data to be used quantitatively in this risk
assessment.
110
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4.3.2 Toxicity to Mammals
4.3.2.1 Mammals: Acute Exposure (Mortality) Studies
Eight laboratory rat gavage toxicity studies for various forms of 2,4-D were submitted to
the Agency. Six studies had definitive LD50s ranging from 441 to 749 mg a.e./kg-bw; one
study had a non-definitive LD50 > 579 mg a.e./kg-bw. One study was not included in the
summary as it was conducted with an end-use product that contained a mixture of two
active ingredients (2,4-D EHE and 2-ethylhexyl ester of 2-(2,4-
dichlorophenoxy)propionic acid).
4.3.2.2 Mammals: Chronic Exposure (Growth, Reproduction) Studies
One two-generation reproductive study (laboratory rat) was submitted to the Agency
using 2,4-D acid. This study resulted in a NOAEC of 5 mg a.e./kg-bw based on the
parental effects of decreased female body weight gain (Fl) and male renal tubule
alteration (FO and Fl)and the offspring effects of decreased pup body weight.
Reproductive effects had a NOAEC of 20 mg a.e./kg-bw based on increased gestation
time.
4.3.2.3 Mammals: Open Literature Data
None of the ECOTOX or open literature data provided acute or chronic toxicity
information that was more sensitive than those values reported in the registrant-submitted
data.
Several mammalian reproductive studies were available in ECOTOX. Although some
toxicity values were more sensitive than registrant-submitted values, most were not
scientifically sound or did not provide sufficient data to be used quantitatively in this risk
assessment.
In a study conducted using male Swiss mice (E93505), the NOAEC for 2,4-D acid was
established at 1.7 mg a.e./kg-bw due to increases in chromosome aberrations in bone
marrow and spermatocyte cells at higher doses (administered via oral gavage for up to
five consecutive days). 2,4-D acid induced a dose-dependent increase in the percentage of
sperm-head abnormalities; a NOAEC was established at 3.3 mg a.e./kg-bw (doses
administered via oral gavage for five consecutive days). This study was not utilized for
risk estimation as frank reproductive effects were not evaluated. However, it does
indicate that genotoxic effects may occur at doses lower than the NOAEC established in
the 2-generation reproduction study submitted by the registrant.
Also in this study (E93505), genotoxic effects were evaluated for the degradate, 2,4-DCP.
Results indicated that the genotoxic effect of 2,4-DCP was weaker than that of 2,4-D.
Statistically-significant increases in chromosome aberrations in bone marrow and in
spermatocyte cells as well as increases in sperm-head abnormalities were observed
111
-------
following a single ip injection of 2,4-DCP at 180 mg/kg-bw. No other statistically-
significant differences from the controls were indicated at the lower treatment levels.
4.3.3 Toxicity to Terrestrial Invertebrates
4.3.3.1 Terrestrial Invertebrates: Acute Contact Studies
Two honey bee acute contact studies were submitted to the Agency. For DMA and EHE,
the studies resulted in LD50s >83 and >66 jag a.e./bee, respectively. Percent mortality
ranged from 1 to 3% in the DMA study, and from 1 to 35% in the EHE study.
4.3.3.2 Terrestrial Invertebrates: Open Literature Data
A study (E39264; Wahl and Ulm, 1983) found in ECOTOX was conducted in Germany
in the early 1970's evaluating the effects of the feed quality of young bees and their
ability to resist toxic effects of twenty formulations of various pesticides. The purpose of
the study was to determine if a rich supply of higher protein feed fed to young bees
would cause them to be less sensitive (higher LD50's) than bees fed a lower quality
(lower protein) diet. Although this study had several variables and was meant to explore
causes of observed bee mortality rather than to establish the acute toxicity value of a
chemical, it does provide useful information about bees' toxic response when exposed to
2,4-D residues via consumption of contaminated food sources.
The authors studied the effects of several types of pollen fed in varying quantities (high
quality food sources), as well as dried skim milk and sugar feed (low quality food
sources). Because the OPPTS 850.3020 guideline study requires bees to be fed a diet of
sugar water, the LD50's from this food type are relevant. The authors observed LD50's of
34.3 jag a.e./bee and 39.5 jag a.e./bee when fed sugar water and a 2,4-D Na end-use
product. This study will be used to qualitatively characterize risk as EFED does not
currently have methods to estimate bee exposure through ingestion.
Toxicity of 2,4-D acid and the degradate 2,4-DCP to mature earthworms (Eisenia foetida)
was evaluated by Roberts and Dorough (E040531; 1984). 2,4-DCP was found to be more
toxic to earthworms than the parent 2,4-D acid with LCso's of 4.4 (95% CI: 3.2-5.9)
Hg/cm2 and 61.6 (95% CI: 41.0-92.4) |j,g/cm2, respectively, in a 48-hr study. This study
will be used to qualitatively characterize risk.
4.3.4 Toxicity to Terrestrial Plants
Plant toxicity data from both registrant-submitted studies and studies in the scientific
literature were reviewed for this assessment. No open literature data presented more
sensitive results than those submitted by the registrants. Registrant-submitted studies are
conducted under conditions and with species defined in EPA toxicity test guidelines.
Sub-lethal endpoints such as plant growth, dry weight, and biomass are evaluated for
both monocots and dicots, and effects are evaluated at both seedling emergence and
vegetative life stages. Guideline studies generally evaluate toxicity to ten crop species. A
112
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drawback to these tests is that they are conducted on herbaceous crop species only, and
extrapolation of effects to other species, such as the woody shrubs and trees and wild
herbaceous species, contributes uncertainty to risk conclusions.
Commercial crop species have been selectively bred and may be more or less resistant to
particular stressors than wild herbs and forbs. The direction of this uncertainty for
specific plants and stressors, including 2,4-D, is largely unknown. Homogenous test
plant seed lots also lack the genetic variation that occurs in natural populations, so the
range of effects seen from tests is likely to be smaller than would be expected from wild
populations.
The results of the Tier II seedling emergence and vegetative vigor toxicity tests on non-
target plants are summarized in Appendix F. Tables F16 to F19 contain summary data
for the most sensitive monocot and dicot endpoint for all seedling emergence and
vegetative vigor studies conducted using technicals of various forms of 2,4-D. Tables
containing results of all species tested using the technicals are provided in the EFED
chapter of the 2,4-D RED.
Since the RED's completion, terrestrial plant studies were submitted to the Agency for
end-use products of 2,4-D DMA and 2,4-D EHE. A summary of results for all species are
contained in Tables F20 to F23. The most sensitive species and endpoints from these
studies will be used for risk estimation. As the studies were conducted with an end-use
product, the exposure to the plants in the study will be similar to exposure to plants in the
environment. Current study guidelines recommend using an end-use product for this
reason. Adjuvants, surfactants, and other inactive ingredients have the potential to
increase the toxicity of the active ingredient, relative to the effect of the active ingredient
alone.
There did not appear to be any systematic differences in toxicity between the evaluated
acid, salts, and esters for either the tests conducted using the technical or the tests
conducted using the end-use products. Therefore, data from end-use product DMA
studies and the end-use product EHE studies will be bridged and the most sensitive
species and endpoints will be used for risk estimation.
In the RED assessment, risk estimation was conducted separately for the acid/salts and
for the esters as differences in solubilities led to different inputs in the TerrPlant
estimation program. Because there was no evidence of difference in toxicity since the
salts dissociate to the acid very quickly (e.g., 2,4-D amine salt dissociates in < 3 minutes)
and the esters hydrolyze to the acid reasonably quickly (e.g., 2,4-D esters in normal
agriculture soil and natural water are short lived compounds, < 2.9 days), EFED will
bridge the toxicity and the exposure estimation for terrestrial plants in this assessment.
4.4 Incident Database Review
A review of the EIIS database for ecological incidents involving 2,4-D acid, salts, and
esters (PC Codes 030001, 030004, 030016, 030019, 030025, 030035, 030053, 030063
113
-------
and 030066) was completed on December 16, 2008. A complete list of the incidents
involving 2,4-D (acid, salts, and esters), including associated uncertainties, is included as
Appendix H.
4.4.1 Terrestrial Incidents
Seven incidents for 2,4-D acid were reported for mammal and bird mortalities, which
included multiple species, from 1991 - 2007 for uses on corn, agricultural areas, right-of-
ways, turf/residential, home/lawn, and sunflowers (Table 4.5). Two of these incidents
were the results of accidental misuse, and one report did not file a specific use. Mortality
incidents were reported from exposure through drift and runoff, and one incapacitation
incidence was reported from exposure through ingestion.
Based on three incident reports 2,4-D has been implicated as being toxic to mammals
with possible and probable certainty for registered and undetermined use legalities.
In one incident report 2,4-D has been implicated as being toxic to birds with probable
certainty for an undetermined use legality.
Table 4.5 Summary ol* 2.4-1) Terrestrial Incidents in 111 IS Database
I so Site/
l.oi'iiiion/Yi'iir
Incidi'iil II)
l.i*U;ilil>
( oi l;iinl>
Species
MiiUiiiliidi'
Response
l'l\|)OMiri'
Agricultural
Area
(Washington,
UT) 1992
1000309-001
Undetermined
Possible
Chipmunk
Numerous
Mortality
Ingestion
Dog
6
Mortality
Ingestion
Horse
1
Incapacitation
Ingestion
Horse
6
Mortality
Ingestion
Squirrel
Numerous
Mortality
Ingestion
Agricultural
Area
(IL)
1970
B000150-002
Registered
use
Probable
Fox
Squirrel
2
Mortality
Runoff
Corn
(Des Moines,
IA) 1996
1004495-001
Misuse
(accidental)
Highly
Probable
Unknown
bird
Unknown
Mortality
Drift
N/R
(Durham, NC)
1992
1000008-001
Misuse
(accidental)
Unlikely
Bluebird
3 nests Ml
Mortality
N/R
Sunflower
(Lincoln, CO)
2006
1017576-001
Registered
use
Unlikely
American
kestrel
1
Mortality
Ingestion
American
robin
1
Mortality
Ingestion
Common
grackle
5
Mortality
Ingestion
Horned
lark
597
Mortality
Ingestion
114
-------
Table 4.5 Summary of 2.4-1) Terrestrial Incidents in 111 IS Database
I so Site/
l.oi'iiiion/Yi'iir
Incidi'iil II)
l.i*U;ilil>
( oi l;iinl>
Species
MiiUiiiliidi'
Response
l'l\|)OMiri'
Kangaroo
rat
Unknown
Mortality
Ingestion
Lark
bunting
Few
Mortality
Ingestion
Mourning
dove
1633
Mortality
Ingestion
Red-
winged
blackbird
5
Mortality
Ingestion
Sparrow
12
Mortality
Ingestion
Unknown
bird
150
Mortality
Ingestion
Western
meadow-
lark
5
Mortality
Ingestion
Turf
residential
(Lancaster,
Pa)
2007
1019025-039
Undetermined
Possible
Rabbit
4
Mortality
Ingestion
Home/Lawn
(Alamance,
NC)
1991
1000799-003
Undetermined
Probable
Blackbird
Unknown
Mortality
Ingestion
Bream
Hundreds
Mortality
Runoff
Cardinal
Unknown
Mortality
Ingestion
Duck
Hundreds
Mortality
Ingestion
Turkey
Unknown
Mortality
Ingestion
4.4.2 Plant Incidents
For 2,4-D, 358 incidents were reported for mostly plant damage to a wide variety of
terrestrial plants particularly from direct treatment or spray drift. For 2,4-D, 140 of the
358 incidents reported were registered uses and 143 were of unknown legality. The
majority of the reports were of possible to highly probable certainty. Other reported
incident exposures included spills, stunted growth, discoloration, runoff, persistence in
crop and carryover. Other reported incident exposures included spills, stunted growth,
discoloration, runoff, persistence in crop and carryover. The majority of the reports were
filed from 1990 - 2007. Only ten reports were filed prior to 1990.
For the 2,4-D acid, 269 incident reports were filed for a wide variety of terrestrial plants,
particularly for uses on home/lawn, residential turf, corn, agricultural areas and right-of-
ways. Other incidents included uses on barley, bean, cotton, orchard, ornamentals,
pasture, pinto bean, potato, rangeland, rice, soybean, switch grass, tree farm, trees, wheat,
yard, driveway, fence row, fields, grass, hay, hillside, municipal operations, and
municipal sites. The reports were filed from 1949 - 2006 (only 10 reports were filed prior
to 1990) with 66 misuses, 103 registered uses, and 100 uses of unknown legality. Plant
damage, browning, and mortality were the main issues with drift and direct treatment as
the main exposure routes.
115
-------
For the 2,4-D DMA salt, 73 incident reports were filed for a wide variety of terrestrial
plants, particularly for uses on home/lawn. Other incidents included uses on utility right-
of-ways, rail right-of-ways, conservation reserve, rhododendron, yard and agricultural
areas. The reports were filed from 1992 - 2002 with 7 accidental misuses, 25 registered
uses, and 41 uses of unknown legality. Plant damage and mortality were the main issues
with drift and direct treatment as the main exposure routes. Browning occurred for only
one incident.
Fifteen incidents occurred for all other salts reported for 2,4-D which included 13
incidents for TIPA salt, 1 incident for DEA salt, and 1 incident for IPA salt. The above
incidents were filed from 1993 -2007 with 2 misuses, 11 registered uses, and 2 uses of
unknown legality. Incidents for TIPA salt were filed on a variety of terrestrial plants for
uses on agricultural area, brome, corn fields, hay, pasture, peanut, rangeland, and
soybean. Plant damage and mortality were the main issues with drift, direct treatment,
persistence on crops, and carryover as exposure routes. Incidents for DEA salt and IPA
salt were filed for uses on agricultural area and milo, respectively. No exposure route
was reported for milo use; however, the agricultural area incident was due to drift
exposure.
Only one incident was reported for 2-EHE ester, which was filed in 1998 as a registered
use. Plant damaged occurred with drift as the main exposure route.
4.4.3 Aquatic Incidents
Twenty-six incidents were filed for 2,4-D acid, and 3 incidents were filed for 2,4-D
DMA salt. The reports were filed from 1970 - 1997 with 5 misuses, 9 registered uses, 3
spills, and 12 uses of unknown legality. Out of 26 incidents reported for aquatic
organisms for 2,4-D acid and DMA salt, six registered uses were reported with
certainties of highly probable(2), probable(2) and possible (2). Incidences for 2,4-D were
filed on aquatic organisms from runoff or drift.
All incidents resulted in mortality of aquatic organisms exposed to 2,4-D from runoff or
drift. Incidents for 2,4-D were filed on aquatic organisms, which included the following
species: Greengill, largemouth bass, bass, silver minnow, smallmouth bass, sunfish,
catfish, crappie, perch, bream croaker, spot tail bass, carp, gizzard shad, salmon,
American eel, blacknose dace, notropis minnow, minnow, white sucker, bluegill, mullet,
drum, garfish, perch, crab, and watersnake. Use sites for the above aquatic organisms
were reported on home/lawn, corn, agricultural areas, right-of-ways/railroad, lake, pond,
spills, stream, sugar cane, tobacco, turf/golf course, athletic fields. Nine use sites were
not reported.
116
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5. Risk Characterization
Risk characterization is the integration of the exposure and effects characterizations. Risk
characterization is used to determine the potential for direct and/or indirect effects to the CRLF
and AW or for modification of their designated critical habitats from the use of 2,4-D in CA.
The risk characterization provides an estimation (Section 5.1) and a description (Section 5.2)
of the likelihood of adverse effects; articulates risk assessment assumptions, limitations, and
uncertainties; and synthesizes an overall conclusion regarding the likelihood of adverse effects
to the assessed species or their designated critical habitats {i.e., "no effect," "may affect and
likely to adversely affect," or "may affect but not likely to adversely affect").
5.1 Risk Estimation
Risk is estimated by calculating the ratio of exposure to toxicity. This ratio is the risk
quotient (RQ), which is then compared to pre-established acute and chronic levels of
concern (LOCs) for each category evaluated (Appendix I). For acute exposures to the
aquatic animals, as well as terrestrial invertebrates, the LOC is 0.05. For acute exposures
to the birds (and, thus, reptiles and terrestrial-phase amphibians) and mammals, the LOC
is 0.1. The LOC for chronic exposures to animals and acute exposures to plants is 1.0.
Acute and chronic risks to aquatic organisms are estimated by calculating the ratio of
exposure to toxicity using l-in-10 year EECs based on the label-recommended 2,4-D
usage scenarios summarized in Tables 3.4 and 3.5 and the appropriate aquatic toxicity
endpoint from Tables 4.1.a and 4.1.b. Acute and chronic risks to terrestrial animals and
plants are estimated based on exposures resulting from applications of 2,4-D (Tables
3.7.a, 3.7.b, 3.8 and 3.9) and the appropriate toxicity endpoint from Table 4.3.
5.1.1 Exposures in the Aquatic Habitat
5.1.1.1 Direct Effects to Aquatic-phase CRLF
Because the AW is a terrestrial organism given its designated critical habitat as well as its
prey base, the aquatic assessment does not include direct or indirect effects to the AW.
Direct effects to the aquatic-phase CRLF are based on peak EECs in the standard pond
and the lowest acute toxicity value for freshwater fish. Separate RQs were calculated for
the acid/salts (runoff+drift) and the esters (drift only and drift+runoff). In addition, risks
to the aquatic-phase CRLF were estimated for direct applications to water. In order to
assess direct chronic risks to the CRLF, 60-day EECs and the lowest acid/salts chronic
toxicity value for freshwater fish were used. Due to the improbability of long-term
exposures (see Environmental Fate Strategy in Section 2.4.1), chronic risks of esters
were not estimated.
Acute and chronic RQ values did not exceed the acute LOC (0.05) and the chronic LOC
(1.0) in any of the acid/salts modeled scenarios or drift only ester modeled scenarios.
(Appendix M). For drift+runoff ester uses, only one scenario had an RQ that met the
117
-------
acute LOC; aerial Forestry and Tree and Brush Control uses (modeled by the CA
Forestry RLF scenario) produced an RQ of 0.05 at the rate of 1 application at 4 lb
a.e./acre (Table 5.1.a) For direct applications to water, the rice and aquatic weed control
acid/salt and ester use RQs exceeded the acute LOC with RQs ranging from 0.06 to 15.38
(Table 5.1.b) Table 5.1.c summarizes the individual effect probabilities for the aquatic-
phase CRLF, to represent 2,4-D acid, salt, and ester uses. Based on the LOC exceedances
for scenarios listed in Tables 5.1.a through 5.1.c, there is potential for 2,4-D uses to
directly affect the aquatic phase of the CRLF.
Table 5.1.a Acute UQs lor freshwater lish based on KIX s lor (Irirt+riinolT used to
represent 2.4-1) ester uses'
Master l.ahcl I se
(LI IE, L5EE)
PRZM/I'.XAMS
Scenario
(I'irsl app dale)
Method2
Application Kate'
Peak
l.l.(
(H&'L)
Acute
RQ
Non-agricultural Uses
Forestry, Tree and Brush
Control
CA Forestry RLF
(1-Mar)
G
1 app 'a 4 lb a.e./acre
7.1353
0.03
A
1 app (3> 4 lb a.e./acre
13.249
0.05*
*LOC exceedances (acute RQ > 0.05) are bolded. Acute RQ = use-specific peak EEC / 0.26 mg a.e./L
(MRID 439307-01, 439103-01). The most sensitive 2,4-D ester toxicity values were bridged for all use
scenarios to calculate RQs.
Chronic EECs are not modeled in this scenario because the hydrolysis soil slurry data indicate that
dissipation in a non-sterile water body will occur at all PHs and therefore long-term exposures are unlikely.
2G = ground application. A = aerial application. All applications are liquid unless otherwise specified.
3Esters are not persistent; only one application modeled due to rapid hydrolysis of EHE to the acid form.
Tabic 5.1.1) Acute and chronic KQs lor freshwater fish based on KKCs for direct
application 1o water to represent 2.4-1) acid. salt, and cslcr uses
Master l.ahcl I se
Calesion
Model
Scenario
Method2
Application Kale
Peak
r.r.c
(llli/l.l
(>0-da\
r.r.c
(fiii/i.)
Acute
RQ
Chronic
RQ
Rice
(acid and salts)
Direct water
applications
G & A
1 app @ 1.5 lb a.e./ acre
I4862
N/A
0.06*
0.11
Aquatic Weed
Control (surface
application or
subsurface injection)
(acid and salts)
Direct water
applications
G & A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
40003
2610
0.17*
0.18
Aquatic Weed
Control (surface
application or
subsurface injection)
(esters only)
Direct water
applications
G & A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
40003
2610
15.38*
NA5
Aquatic Weed
Control
(esters only)
Direct water
applications
G & A
2 app @2 lb a.e./acre
(30-day interval)
740
483
2.9*
NA5
118
-------
Table 5.1.1) Acute and chronic KQs lor I'reshwsiter I'isli based on 111
;i|)|)liciilion lo wilier lo represent 2.4-1) acid. salt. and ester uses
.( s lor direct
Master l.ahcl I so
( alexin
Model
Scenario
Method2
Application Kale
Peak
l.l.(
(fiti/l.)
Ml-daj
i r.c
i.uii/1.)
Acute
RQ
Chronic
RQ
Aquatic Weed
Control
(acid and salts)
Direct water
applications
G & A
2 app @ 4 lb a.e./ acre
(21-day interval)
1480
966
0.06*
0.07
Aquatic Weed
Control
(esters only)
Direct water
applications
G & A
2 app @ 4 lb a.e./ acre
(21-day interval)
1480
966
5.7*
NA4
* LOG' exceedances (acute RQ > 0.05; chronic RQ > 1.0) are bolded. Acute RQ (acid and salts) = use-specific
peak EEC / 24.15 mg a.e./L (E006387). Chronic RQ (acid and salts) = use-specific 60-day EEC /14.2 mg a.e./L
(MRID 417677-01). Acute RQ (esters) = use-specific peak EEC / 0.26 mg a.e./L (MRID 439307-01, 439103-
01).
'G = ground application. A = aerial application. All applications are liquid unless otherwise specified.
2Rice Model - the maximum water surface concentration is used to determine both acute and chronic toxicity.
3Aquatic weed control-peak water concentration: 4000 |ig/L , 21-day average water concentration: 3417 |ig/L.
and 60-day average water concentration: 2610 |ig/L. For ester direct application scenarios, 2,4-D acid input
parameters were used to determine EEC. All other runoff and drift application scenarios used 2,4-D ester input
parameters to determine EEC.
4Chronic EECs are not modeled in this scenario because the hydrolysis soil slurry data indicate that dissipation
in a non-sterile water body will occur at all pHs and therefore long-term exposures are unlikely.
Table 5.1.c Summary of Direct K ITcd KQs lor 1 lie Aquatic-phase ( KM- . Individual
KITcct Probabilities to represent 2.4-1) acid. suit, and ester uses
Scenario
Method2
Application Kale
Direct
1. fleets
Acute RQ*
Probability of lndi\ idual
I".ITect at RQi4
(Confidence Interval)
Non-agricultural Uses
Forestry, Tree and
Brush Control
(esters only)
G/A
1 app @ 4 lb a.e./acre
0.05*
1 in 8.29E+42
(6.05, 15.18)
Direct application to water Uses
Rice
(acid and salts)
G & A
1 app @ 1.5 lb a.e./ acre
0.06*
1 in 1.02E+38
(6.05, 15.18)
Aquatic Weed
Control (surface
application or
subsurface injection)
(acid and salts)
G/A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
0.17*
1 in 3.74E+03
(2, 9)
Aquatic Weed
Control (surface
application or
subsurface injection)
(esters only)
G/A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
15.38*
1 in 1.00E+00
(6.05, 15.18)
Aquatic Weed
Control
(esters only)
G/A
2 app @2 lb a.e./acre
(30-day interval)
2.9*
1 in 1.00E+00
(6.05, 15.18)
119
-------
Table 5.1.c Summary of Direct Kfl'ect KQs for llic Aquatic-phase ( KM-1. Individual
KITcct Probabilities to represent 2.4-1) acid. salt, and ester uses
Scenario
\lc(hod:
Application Kale
Direcl
r.lTecls
Acule UQ
PmhahiliM of lndi\ idual
r.lTccl al UQ14
(Confidence Inlcnal)
Aquatic Weed
Control
(acid and salts)
G/A
2 app @ 4 lb a.e./ acre
(21-day interval)
0.06*
1 in 1.02E+38
(6.05, 15.18)
Aquatic Weed
Control
(esters only)
G/A
2 app @ 4 lb a.e./ acre
(21-day interval)
5.7*
1 in 1.00E+00
(6.05, 15.18)
*LOC exceedances (acute RQ > 0.05) are bolded. Acute RQ (acid and salts) = use-specific peak EEC /
24.15 mg a.e./L (E006387). Acute RQ (esters) = use-specific peak EEC / 0.26 mg a.e./L (MRID 439307-
01,439103-01).
1 RQs associated with acute and chronic direct toxicity to the CRLF are also used to assess potential indirect
effects to the CRLF based on a reduction in freshwater fish and frogs as food items
2G = ground application. A = aerial application. All applications are liquid unless otherwise specified.
3A probit slope and 95% confidence interval for the acute bluegill toxicity test for ester was available;
therefore, the effect probability was calculated based on slope of 10.61 with a 95% confidence interval of
(6.05, 15.18).
4A probit slope for the common carp toxicity test (acid and salts) was not available; therefore, the effect
probability was calculated based on the default slope of 4.5 with a 95% confidence interval of (2, 9).
5.1.1.2 Indirect Effects to Aquatic-Phase CRLF via Reduction
in Prey (Non-vascular Aquatic Plants, Aquatic
Invertebrates, Fish, and Frogs)
5.1.1.2.1 Non-vascular Aquatic Plants
Indirect effects of 2,4-D to the aquatic-phase CRLF (tadpoles) via reduction in non-
vascular aquatic plants in its diet are based on peak EECs from the standard pond and the
lowest toxicity value (EC50) for aquatic non-vascular plants.
There were no LOC exceedances except for direct applications to water uses. All RQs are
provided in Appendix M, RQs resulting in LOC exceedances are provide in Table 5.2.
These direct applications to water have the potential to indirectly affect the aquatic-phase
CRLF through a reduction in food sources.
120
-------
Table 5.2 UQs lor non-vascular plants based on KKCs lor direct application to
water to represent 2.4-1) acid. salt, and ester uses
Master l.ahel I so
( alexin
Model
Scenario
Method1
Application Kale
Peak
r.r.c
(llli/l.l
RQ
Aquatic Weed Control
(surface application or
subsurface injection)
(acid and salts)
Direct water
applications
G & A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
40002
1.03*
Aquatic Weed Control
(surface application or
subsurface injection)
(esters only)
Direct water
applications
G & A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
40002
60.61*
Aquatic Weed Control
(esters only)
Direct water
applications
G & A
2 app @ 2 lb a.e./acre
(30-day interval)
740
11.21*
Aquatic Weed Control
(esters only)
Direct water
applications
G & A
2 app @ 4 lb a.e./ acre
(21-day interval)
1480
22.42*
*LOC exceedances (RQ > 1.0) are bolded. RQ (acid and salts) = use-specific peak EEC / 3.88 mg a.e./L
(MRID 415059-03). RQ (esters) = use-specific peak EEC / 0.066 mg a.e./L (MRID 417352-04).
'G = ground application. A = aerial application. All applications are liquid unless otherwise specified.
2Aquatic weed control-peak water concentration: 4000 |ig/L , 21-day average water concentration: 3417
|ig/L. and 60-day average water concentration: 2610 |ig/L. For ester direct application scenarios, 2,4-D acid
input parameters were used to determine EEC. All other runoff and drift application scenarios used 2,4-D
ester input parameters to determine EEC.
5.1.1.2.2 Aquatic Invertebrates
Indirect acute effects to the aquatic-phase CRLF via effects to prey (invertebrates) in
aquatic habitats are based on peak EECs in the standard pond and the lowest acute
toxicity value for freshwater invertebrates. Separate RQs were calculated for the
acid/salts (runoff+drift) and the esters (drift+runoff and drift only). In addition, indirect
risks to the aquatic-phase CRLF were estimated for direct applications to water. For
chronic risks, 21-day EECs and the lowest chronic toxicity value for invertebrates were
used to derive RQs for acid/salt uses. Due to the improbability of long-term exposures
(see Environmental Fate Strategy in Section 2.4.1), chronic risks of exposure to esters
were not estimated.
There were no acute or chronic LOC exceedances for acid/salt uses, drift+runoff ester
uses, and drift only ester uses (Appendix M). For direct applications to water, rice and
the aquatic weed control acid/salt and ester use RQs exceeded the acute LOC (Table
5.3.a),
121
-------
Based on the results of probit analysis in Table 5.3.b, there is a significant chance (>
10%) that direct applications to water (aquatic weed control ester uses) will impact prey
of the CRLF via direct effects on aquatic invertebrates as dietary food items. Based on
the LOC exceedances and the results of the probit analysis, there is potential for 2,4-D
uses to indirectly affect the aquatic phase of the CRLF through a reduction in invertebrate
prey.
Table 5.3.SI Acute and chronic UQs lor freshwater invertebrates based on KKC*
lor direct
application to water to represent 2.4-
) acid. salt, and ester uses
Master l.ahel I se
Calejion
Model
Scenario
Method1
Application Kale
Peak
r.r.c
21-daj
r.r.c
Acute
RQ
Chronic
RQ
(llli/l.l
(fiii/t.)
Rice
(acid and salts)
Direct
water
applications
G & A
1 app @ 1.5 lb a.e./acre
I4862
N/A
0.06*
0.09
Aquatic Weed
Control (surface
application or
subsurface injection)
(acid and salts)
Direct
water
applications
G & A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
40003
3417
0.16*
0.21
Aquatic Weed
Control (surface
application or
subsurface injection)
(esters only)
Direct
water
applications
G & A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
40003
3417
1.82*
NA4
Aquatic Weed
Control
(esters only)
Direct
water
applications
G & A
2 app @2 lb a.e./acre
(30-day interval)
740
632
0.34*
NA4
Aquatic Weed
Control
(acid and salts)
Direct
water
applications
G & A
2 app @ 4 lb a.e./ acre
(21-day interval)
1480
1264
0.05*
0.07
Aquatic Weed
Control
(esters only)
Direct
water
applications
G & A
2 app @ 4 lb a.e./ acre
(21-day interval)
1480
1264
0.67*
NA4
* LOC exceedances (acute RQ > 0.05; chronic RQ > 1.0) are bolded. Acute RQ (acid and salts) = use-specific peak
EEC / 25 mg a.e./L (MRID 411583-01). Chronic RQ (acid and salts) = use-specific 21-day EEC /16.05 mg a.e./L
(MRID 420183-03). Acute RQ (esters) = use-specific peak EEC / 2.2 mg a.e./L (MRID 439306-01).
'G = ground application. A = aerial application All applications are liquid unless otherwise specified.
2Rice Model - the maximum water surface concentration is used to determine both acute and chronic toxicity.
3Aquatic weed control-peak water concentration: 4000 |ig/L , 21-day average water concentration: 3417 ng/L, and 60-
day average water concentration: 2610 ng/L. For ester direct application scenarios, 2,4-D acid input parameters were
used to determine EEC. All other runoff and drift application scenarios used 2,4-D ester input parameters to determine
EEC.
4Chronic EECs are not modeled in this scenario because the hydrolysis soil slurry data indicate that dissipation in a
non-sterile water body will occur at all PHs and therefore long-term exposures are unlikely.
122
-------
Table 5.3.b Summary of Acute UQs I sed to l.slimale Indirect K fleets to the CULK
via Direct K fleets on Aquatic Invertebrates as Dietary Kood Items (prev ol'CUI.I'"
juveniles and adults in aquatic habitats). Percent KITcct Probabilities
Master l.ahel I so
Model
Scenario
Method1
Application Kale
Acule UQ
"i. r.lTocl al
Rice
(acid and salts)
Direct
water
applications
G & A
1 app @ 1.5 lb a.e./acre
0.06*
2%
Aquatic Weed
Control (surface
application or
subsurface injection)
(acid and salts)
Direct
water
applications
G & A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
0.16*
9%
Aquatic Weed
Control (surface
application or
subsurface injection)
(esters only)
Direct
water
applications
G & A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
1.82*
88%
Aquatic Weed
Control
(esters only)
Direct
water
applications
G & A
2 app @2 lb a.e./acre
(30-day interval)
0.34*
2%
Aquatic Weed
Control
(acid and salts)
Direct
water
applications
G & A
2 app @ 4 lb a.e./ acre
(21-day interval)
0.05*
1%
Aquatic Weed
Control
(esters only)
Direct
water
applications
G & A
2 app @ 4 lb a.e./ acre
(21-day interval)
0.67*
22%
*LOC exceedances (acute RQ > 0.05; Acute RQ (acid and salts) = use-specific peak EEC / 25 mg a.e./L
(MRID 411583-01). Acute RQ (esters) = use-specific peak EEC / 2.2 mg a.e./L (MRID 439306-01).
'G = ground application. A = aerial application. All applications are liquid unless otherwise specified.
2 For acid/salts, a probit slope and 95% confidence interval for the daphnia acute toxicity test was available;
therefore, the effect probability was calculated based on the slope of 1.69 with a 95% confidence interval
of (1.05, 2.34). For esters, a probit slope and 95% confidence interval for the daphnia acute toxicity test
was not available; therefore, the effect probability was calculated based on the default slope of 4.5 with a
95% confidence interval of (2, 9).
5.1.1.2.3 Fish and Frogs
Fish and frogs also represent potential prey items of adult aquatic-phase CRLFs. RQs
associated with acute and chronic direct toxicity to the CRLF (Table 5.1.a and 5.1.b) are
used to assess potential indirect effects to the CRLF based on a reduction in freshwater
fish and frogs as food items. Acute RQ values exceed the acute LOC in a few modeled
scenarios for fish and frogs. Based on the LOC exceedances and the individual effects
analysis listed in Tables 5.1.a through 5.1.c, there is potential for 2,4-D uses to indirectly
affect the aquatic-phase CRLF through a reduction in vertebrate prey (fish and frogs).
123
-------
5.1.1.3 Indirect Effects to CRLF via Reduction in Habitat
and/or Primary Productivity (Freshwater Aquatic
Plants)
Indirect effects to the CRLF via direct toxicity to aquatic plants are estimated using the
most sensitive non-vascular and vascular plant toxicity endpoints. Because there are no
obligate relationships between the CRLF and any aquatic plant species, the most sensitive
EC50 values, rather than NOAEC values, were used to derive RQs.
There were several LOC exceedances for acid/salt uses for vascular aquatic plants (Table
5.4.a), The RQs with LOC exceedances ranged from 1.05 to 3.56. There were no LOC
exceedances for drift+runoff ester uses and drift only ester uses (Appendix M). For
direct applications to water, the rice use and the acid/salt and ester aquatic weed control
RQs exceeded the LOC with RQs ranging from 2.2 to 305.34 (Table 5.4.b), Based on the
LOC exceedances, there is potential for 2,4-D uses to indirectly affect the aquatic-phase
CRLF through a reduction in habitat and/or primary productivity.
Table 5.4.a UQs for vascular plants based 011 KIX s for runoff and drift used to
represent 2.4-1) acid and salt uses
Master l.ahcl I sc
Calcgon
PRZM/EWMS
Scenario
(first app date)
Method'
Application Kale
(inlcnal hclwccn
applications)
Peak
EEC
(Mg'M
no
Orchard Uses
Nut Orchards,
Pistachios
CA Almond wirrig
STD
(10-Feb)
G
2 apps @ 2 lb a.e./acre
(30-day interval)
13.69
1.05*
Agricultural - Food Crop Uses
Sugarcane
CA Sugar beet wirrig
OP (20-Jan)
G
1 pre-emergence and 1
post-emergence app @ 2 lb
a.e./acre
25.85
1.97*
A
1 pre-emergence and 1
post-emergence app @ 2 lb
a.e./acre
33.31
2.54*
Cereal Grains
CA Wheat RLF
(10-Feb)
G
1 post-emergence app @
1.25 lb a.e./acre; 1 pre-
harvest app @ 0.5 lb
a.e./acre
(90-day interval)
21.39
1.63*
A
1 post-emergence app @
1.25 lb a.e./acre,
1 pre-harvest app @ 0.5 lb
a.e./acre
(90-day interval)
23.43
1.79*
Grain or Forage
Sorghum
CA Wheat RLF
(10-Feb)
G
1 post-emergence app @
1.0 lb a.e./acre
17.00
1.30*
A
1 post-emergence app @
1.0 lb a.e./acre
18.61
1.42*
Asparagus
CA Row Crop RLF
(1-Apr)
G
2 apps @ 2 lb a.e./acre
(30-day interval)
12.62
0.96
124
-------
Tsihle 5.4.;i KQs lor \siseulsir phinls hsised on KIX s lor runolT smd (Irill used lo
represent 2.4-1) sic id smd ssill uses
Masler l.ahcl I sc
PKZM/I.WMS
Scenario
(firs! app dale.)
Mel hod1
Application Kale
(inler\al helween
applications)
Peak
l.l.(
no
A
2 apps (m 2 lb a.c./acrc
(30-dav interval)
20.14
1.54*
Non-agricultural Uses
Non-cropland
CA Right-of-Way RLF
(20-Feb)
G
1 app (3> 4 lb a.e./acre
39.02
2.98*
A
1 app (i 4 lb a.e./acre
46.66
3.56*
Forestry, Tree and
Brush Control
CA Forestry RLF
(1-Mar)
G
1 app 'a 4 lb a.e./acre
15.92
1.22*
A
1 app (i 4 lb a.e./acre
24.98
1.91*
Grass Grown for
Seed and Sod
CA Turf RLF
(1-Mar)
G
2 apps @ 2 lb a.e./acre
(21-day interval)
6.17
0.47
A
2 apps @ 2 lb a.e./acre
(21-day interval)
14.87
1.14*
*LOC exceedances (RQ > 1.0) are bolded. RQ = use-specific peak EEC / 0.0131 mg a.e./L (E74985). The
most sensitive 2,4-D acid and salt toxicity values were bridged for all use scenarios to calculate RQs.
'G = ground application. A = aerial application. All applications are liquid unless otherwise specified.
Tsihle 5.4.1) KQs lor \siscuhir phinls hsised on KIX's lor direct :ipplic:ilion lo wsiler lo
represenl 2.4-1) sir id. ssill. sind esler uses
Masler l.ahcl I se ( aleuorj
Model Scenario
Mel hod'
Application Kale
Peak
r.r.c
(flii/l.)
HQ
Rice
(acid and salts)
Direct water
applications
G & A
1 app @ 1.5 lb a.e./acre
1486
113*
Aquatic Weed Control
(surface application or
subsurface injection for
submersed weeds)
(acid and salts
Direct water
applications
G & A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
40002
305.34*
Aquatic Weed Control
(surface application or
subsurface injection for
submersed weeds)
(esters only)
Direct water
applications
G & A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
40002
12.12*
Aquatic Weed Control
(acid and salts)
Direct water
applications
G & A
2 app @2 lb a.e./acre
(30-day interval)
740
56.49*
Aquatic Weed Control
(esters only)
Direct water
applications
G & A
2 app @2 lb a.e./acre
(30-day interval)
740
2.2*
Aquatic Weed Control
(acid and salts)
Direct water
applications
G & A
2 app @ 4 lb a.e./ acre
(21-day interval)
1480
112.98*
125
-------
Table 5.4.1) UQs for vascular plants based on K
represent 2.4-1) acid. salt, and ester uses
X s for direct application to water to
Master l.ahcl I sc ( alciion
Model Scenario
Method'
Application Kale
Peak
l.l.(
(flli/l.)
RQ
Aquatic Weed Control
(esters only)
Direct water
applications
G & A
2 app @ 4 lb a.e./ acre
(21-day interval)
1480
4.48*
*LOC exceedances (RQ > 1.0) are bolded. RQ (acid and salts) = use-specific peak EEC / 0.0131 mg a.e./L
(E74985). RQ (esters) = use-specific peak EEC / 0.33 mg a.e./L (MRID 417352-03).
'G = ground application. A = aerial application.
2Aquatic weed control-peak water concentration: 4000 |ig/L , 21-day average water concentration: 3417
|ig/L and 60-day average water concentration: 2610 |ig/L. For ester direct application scenarios, 2,4-D acid
input parameters were used to determine EEC. All other runoff and drift application scenarios used 2,4-D
ester input parameters to determine EEC.
5.1.2 Exposures in the Terrestrial Habitat
5.1.2.1 Direct Effects to Terrestrial-phase CRLF and AW
(Birds Used as Surrogate for Reptiles and Terrestrial-
phase Amphibians)
As previously discussed in Section 3.3, potential direct effects to terrestrial species are
based on foliar applications and granular applications of 2,4-D. Potential risks to birds
(and, thus, reptiles and terrestrial-phase amphibians) are derived using T-REX, acute and
chronic toxicity data for the most sensitive bird species for which data are available, and
a variety of body-size and dietary categories.
Potential direct acute effects to the terrestrial-phase CRLF and AW due to liquid
applications of 2,4-D are derived by considering dose- and dietary-based EECs modeled
in T-REX for a small bird (20 g) consuming small invertebrates and acute oral and
subacute dietary toxicity endpoints for avian species. Acute direct effects to the
terrestrial-phase CRLF and AW via exposure to 2,4-D granules are derived based on
LD50/ft2 values. Sample T-REX modeling results are located in Appendix J.
Potential direct chronic effects of 2,4-D to the terrestrial-phase CRLF and AW are
derived by considering dietary-based exposures modeled in T-REX for birds consuming
small invertebrates.
Based on the results of T-REX, all the modeled liquid applications of 2,4-D except Citrus
and Potatoes exceed the Listed Species LOC for acute risks (direct effects) to the CRLF
and the AW based on an acute oral basis (Table 5.5). The RQs that exceeded the LOC
ranged from 0.39 to 38.67. For granular applications, the Listed Species LOC was
exceeded with RQ values ranging from 2.43 to 130.96 (Table 5.6.a), Individual effect
probabilities are located in Table 5.6.b and are based on the highest liquid or granular
application RQ. Based on the T-REX modeling results, there is one chronic LOC
126
-------
exceedance for 2,4-D use on aquatic weed control via surface application with an RQ of
7 58 (Table 5.5)
The LC50 values for both the Northern bobwhite quail and mallard duck were > 3035 mg
a.e./kg-diet, and no mortalities were observed at the highest test concentration (MRID
416444-02, 416444-03). Therefore, definitive acute dietary RQ values could not be
derived, and the confidence in a risk call for birds is low as there were no mortalities in
the dietary studies. Applying best professional judgment to this situation, considering
both the unknown LC50 and the high uncertainty of any RQ calculated based on this non-
definitive LC50, it is concluded that these birds are not at risk for acute effects based on
the results of the dietary studies.
All the 2,4-D modeled uses except Citrus and Potatoes have the potential to directly
affect the CRLF and AW based on the acute LOC exceedances demonstrated in T-REX.
Based on T-REX, the only use with chronic direct effect concerns is aquatic weed control
via surface application.
Table 5.5 I pper-bonnd kenega Nomogram UQs lor Diclarv-and Dose-based Kxposnres of 1 lie
Terreslrial-phase CUI
.1- and AW and its .Mammalian Prev lo Liquid Applie
ill ions of 2.4-1)
KQs lorCKI.I- and AW
(l)irecl I'.ITcclsr
and
KQs lor Mammalian Prey' (Indirect
KQs lor I-
ro*i Prc\"
e ITec Is
lo CKI.I- and AW)
(Indirect effects lo
Modeling
Scenario
CKI.I- and AW)
Method'
Application Kale
Acule dose-
based
(Small hird
consilium'.:
small
insect 1
Chronic
dicl-hascd
(ISial
aiiisiimnm
small
lllsCCls)
Acule dose-
based
(Small
mammal
aiiisiimiim
sIrii'I mass)
Chronic
dose-
based
Chronic
diel- based
(Small
mammal
aiiisiiminu
slioi l giastj)
(Mammal
aiiisiimiiiu
sIrii'I massi
Orchard Uses
Nut Orchards,
Pistachios
G
2 apps @ 2 lb a.e./acre
(30-day interval)
1.57*
0.31
0.52*
45.57+
5.25+
Filberts
G
4 apps @ 0.5 lb
a.e./acre
(30-day interval)
0.40*
0.08
0.13*
11.49+
1.32+
Grapes (all)
G
1 app @ 1.36 lb
a.e./acre
0.97*
0.19
0.32*
28.32+
3.26+
Blueberries
G
2 apps @ 1.4 lb
a.e./acre (30-day
interval)
1.10*
0.21
0.36*
31.90+
3.68+
Stone and
Pome Fruits
G
2 apps @ 2 lb a.e./acre
(75-day interval)
1.44*
0.28
0.47*
41.76+
4.81+
Citrus
A/G
1 app @ 0.1 lb a.e./acre
0.07
0.01
0.02
2.08+
0.24
Agricultural - Food Crop Uses
Field Corn,
Popcorn
A/G
1 app @ 1.0 lb a.e./acre
March 15,
1 app (a} 0.5 lb a.e./acre
1.08*
0.21
0.35*
31.26+
3.60+
127
-------
Table 5.5 I ppcr-bound kcncgn Nomogram KQs lor Diclnrv-nnd Doso-bsisod Kxposurcs of the
TcitcsI rial-phase C'UI
.!" iiihI AW and ils \l;iiiiin:ili:iii Prcv lo Liquid Applic
ill ions of 2.4-1)
KQs lorCKI.I- and AW
(Direct r.l'l'eclsr
and
KQs lor Mammalian Prey' (Indirccl
KQs lor 1
rog Prej"
effects
loCKI.I- and AW)
(Indirccl cITccls lo
Modeling
Scenario
( Kl.l- and AW)
Melliod1
Application Kale
Acule dose-
based
(Small hi id
aiMsllMHMU
small
insecl)
Chronic
diel-based
iliii'd
a
-------
Tsihle5.5 I pper-hoiind kene»;i Nomogrsim KQs lor Dielsirv-sind Dose-hsised Kxposures of the
Tcrreslrisd-phsise CUI.I'" smd AW smd its M:iiiiin:ili:iii Prev to Liquid Applications of 2.4-1)
KQs lorCKI.I- and AW
(Direct r.lTcctsr
and
KQs lor Mammalian Prey' (Indirect
KQs for 1
rog Prc\"
effects
lo( KM- and AW)
(Indirect effects to
Modeling
Scenario
( Kl.l- and AW)
Method1
Application Kale
Acute dosc-
hascd
(Small hi id
aiMsllMHMU
small
lllsCCl)
Chronic
dicl-hascd
iliii'd
COIISIimiMU
small
illsCCls)
Acute dosc-
hascd
(Small
mammal
COIISIimiMU
shoii mass)
Chronic
dosc-
bascd
(Small
mammal
coMsiimmu
shoii mass)
Chronic
diet- bused
(Mammal
coMsuminu
shoi'i mass)
Control
Ornamental
Turf
A/G
2 apps @ 1.5 lb
a.e./acre
1.28*
0.25
0.42*
37.21+
4.29+
(21-day interval)
Grass Grown
for Seed and
Sod
A/G
2 apps @ 2 lb a.e./acre
(21-day interval)
1.71*
0.33
0.56*
49.61+
5.72+
Direct Application to Water Uses
Rice
A/G
1 app @ 1.5 lb a.e./acre
1.07*
0.21
0.35*
31.23+
3.60+
Aquatic Weed
Control
A/G
1 app @ 10.8 lb
a.e./acre-foot5
38.67*
7.58+
12.75*
1124.41+
129.60+
Aquatic Weed
Control
A/G
2 app @ 2 lb a.e./acre
(30-day interval)
1.57*
0.31
0.52*
45.57+
5.25+
Aquatic Weed
Control
A/G
2 app @ 4 lb a.e./acre
(21-day interval)
3.41*
0.67
1.12*
99.22+
11.44+
'G = ground application. A = aerial application.
2EECs based on small bird (20 g), which consumes small insects.
3EECs based on small mammal (15 g), which consumes short grass.
4These EECs also apply for terrestrial invertebrates (small insects).
5Label states apply 10.8 lb a.e./acre-foot. If water body is 5 ft deep, this equals an application rate of 54 lb a.e/.acre
*Acute (RQ > 0.1) exceeds acute endangered species level of concern (LOC).
+Chronic (RQ > 1.0) exceeds chronic level of concern (LOC).
Tsihle Acute KQs for C>r:iiinl:ir Applications
(lie l errestrinl-phnse CUI.I'" ;ind AW . (2) Indim*
nnd (3) Indirect KITects on (lie l errestrinl-phnsc <
of 2.4-1) for (1)
KITccts on the.
UI.K iind AW
Direct Kfleets on
\W (birds sis prev).
fro«s sire prev)
Scenario
Application Kate
EEC
(mg a.e./ft2)
Acute K<>
(LDso)1
Agricultural Food Crop Uses
Field Corn, Popcorn
1 app @ 1.0 lb a.e./acre March 15,
1 app @ 0.5 lb a.e./acre April 29,
1 app 'a 1.5 lb a.e./acre August 15
15.62
3.64*
Sweet Corn
1 app @ 1 lb a.e./acre March 15; 1
app (i 0.5 lb a.e./acre April 29
10.41
2.43*
Grain or Forage
Sorghum
1 post-emergence app @ 1.0 lb
a.e./acre
10.41
2.43*
129
-------
Tsihlc 5.6.21 Acute UQs lor (.rnnnhir Application
(lie Tcrrcslri;il-|)h;isc CUM'" ;ind AW . (2) Imlim
iind (3) Indirect KITccts on (lie Tcrrcstrhil-phnse
sol"2.4-1) lor(l)
( KITccts on (lie .
CRI.I-'iiml AW
Direct KITccts on
\\\ (birds sis prey).
IVo«s sire prey)
Scenario
Application Kale
EEC
(ni» a.c./l'n
Acute UQ
iLDj,,)1
Non-Agricultural Uses
Non-cropland
1 app 'a 4 lb a.e./acre
41.65
9.70*
Ornamental Turf
2 apps @ 1.5 lb a.e./acre
(21-day interval)
15.62
3.64*
Grass Grown for Seed
and Sod
2 apps @ 2 lb a.e./acre
(21-day interval)
20.83
4.85*
Direct Application to Water Uses
Aquatic Weed Control
1 app (i 10.8 lb a.e./acre-foot
562.30
130.96*
Aquatic Weed Control
2 app @ 2 lb a.e./acre
(30-day interval)
20.83
4.85*
Aquatic Weed Control
2 app @ 4 lb a.e./acre
(21-day interval)
41.65
9.70*
Calculation based on Northern bobwhite quail acute oral dose LD50 =298 mg a.e./kg-bw (MRID 442757-
01).
*Acute RQ > 0.1 exceeds acute listed species level of concern (LOC).
Tsihlc 5.6.h Snin 111:1 r\ of Direct
KITcct Probabilities (hsiscd on (
KITcct UQs lor the TciTcstrisil-phsisc ( KLI- . Individusil
ircct cITcct sicutc UQs presented in Tsibles 5.5 ;ind 5.6si)
Master Label I se
C ;iteii
-------
Table 5.6.1) Suiniiiiirv of Direct
KITccl Probabilities (based on (
KITeot KQs lor (lie Terreslrial-pliase ( KM- . Individual
ireol effect acute KQs presented in Tables 5.5 and 5.6si)
Master l.illK'l I so
( alegon
Applicalion
Tj pe'
Applicalion Kale
(inlenal belween
applicalions)
llighesl
Dose-Based R<>
Probability of
lndi\ idual I'.ITecl al
UQ:
(45-day interval)
Potatoes
Liquid
2 apps @ 0.07 lb a.e./acre
(10-day interval)
NoLOC
exceedance
Sugarcane
Liquid
2 app @ 2 lb a.e./acre
(20-day interval)
1.73
1 in 1.17E+00
Cereal Grains
Liquid
1 post-emergence app @
1.25 lb a.e./acre and 1 pre-
harvest app @ 0.5 lb
a.e./acre
(90-day interval)
0.90
1 in 2.39E+00
Grain or Forage
Sorghum
Granular
1 post-emergence app @1.0
lb a.e./acre
2.43
1 in 1.04E+00
Hops
Liquid
3 apps @ 0.5 lb a.e./acre
(30-day interval)
0.39
1 in 3.04E+01
Asparagus
Liquid
2 apps @ 2 lb a.e./acre
(30-day interval)
1.57
1 in 1.23E+00
Fallowland and
Crop Stubble
Liquid
2 apps @ 2 lb a.e./acre
(30-day interval)
1.57
1 in 1.23E+00
Agricultural - Non-food Crop Uses
Established Grass
Pastures,
Rangeland,
Perennial
Grassland Not in
Agricultural
Production
Liquid
2 apps @ 2 lb a.e./acre
(30-day interval)
1.57
1 in 1.23E+00
Non-agricultural Uses
Non-cropland
Granular
1 app @ 4 lb a.e./acre
9.70
1 in 1.00E+00
Forestry
Liquid
1 app @ 4 lb a.e./acre
2.86
1 in 1.00E+00
Tree and Brush
Control
Liquid
1 app @ 4 lb a.e./acre
2.86
1 in 1.00E+00
Ornamental Turf
Granular
2 apps @ 1.5 lb a.e./acre
(21-day interval)
3.64
1 in 1.01E+00
Grass Grown for
Seed and Sod
Granular
2 apps @ 2 lb a.e./acre
(21-day interval)
4.85
1 in 1.00E+00
Direct Application to Water Uses
Rice
Liquid
1 app (fi), 1.5 lb a.e./acre
1.07
1 in 1.81E+00
Aquatic Weed
Granular
1 app @ 10.8 lb a.e./acre-
130.96
1 in 1.00E+00
131
-------
Table 5.6.1) Summary of Direct
K fleet Probabilities (based on (
KITcd KQs for the Tcrrcslrial-pliasc ( KIT . Individual
irect effect acute KQs presented in Tables 5.5 and 5.6a)
MsiSU'r l.illK'l I so
( ;i(eii»r\
Application
Tj pc1
Applicalion Kale
(inlcnal hclwccn
applications)
Mi'JiesI
l)nse-Based R<>
Prohahilil.t of
lndi\ idual l-llTccl al
UQ:
Control
Surface application
or subsurface
injection
foot
Aquatic Weed
Control
Ditchbank
Granular
2 apps @ 2 lb a.e./acre
(30-day interval)
4.85
1 in 1.00E+00
Aquatic Weed
Control
Surface application
Granular
2 app @ 4 lb a.e./acre
(21-day interval)
9.70
1 in 1.00E+00
1 Liquid or granular, application type listed provided the highest dose-based RQ for each use scenario for "small
birds consuming small insects"
2A slope value was not available for the acute bird of LD50 = 298 mg a.e. /kg-bw bobwhite quail (MRID 442757-
01), therefore the probability was calculated based on the default slope value of 4.5.
5.1.2.2 Indirect Effects to Terrestrial-phase CRLF and AW via
Reduction in Prey (Mammals, Birds, Terrestrial
invertebrates, and Frogs)
5.1.2.2.1 Mammals
Potential risks to mammals are derived using T-REX, acute and chronic rat toxicity data,
and a variety of body-size and dietary categories.
The T-REX Modeling results for liquid applications are presented in Table 5.5. Based on
the T-REX results, all the modeled uses exceed the Agency LOC for acute and chronic
risk to mammals. The acute RQs range from 0.13 to 12.75, and the chronic RQs range
from 1.32 to 1112.41. Indirect effects to terrestrial-phase CRLFs and AW via ingestion of
small mammals that may consume 2,4-D granules are based on LD50/ft2 values. The
Listed Species LOC was exceeded with RQ values ranging from 0.72 to 38.68 for
granular applications of 2,4-D (Table 5.7).
Since the acute and chronic RQs are exceeded, there is a potential for indirect effects to
those listed species that rely on mammals during at least some portion of their life-cycle
{i.e., CRLF and AW through mammalian prey consumption).
132
-------
Table 5.7 Acute UQs used lo Kslimale Indirect effects lo Icrrcslrial-pliasc C'Kl.h's
and AW via ingestion of small mammals thai mav consume 2.4-1) granules
Scenario
Application Kale
i:i:< 1
lm» a.e./1'r)
Acule UQ:
Agricultural Food Crop Uses
Field Corn, Popcorn
1 app @ 1.0 lb a.e./acre
March 15, 1 app @ 0.5
lb a.e./acre April 29, 1
app @ 1.5 lb a.e./acre
August 15
15.62
1.07*
Sweet Corn
1 app @ 1 lb a.e./acre
March 15; 1 app @ 0.5
lb a.e./acre April 29
10.41
0.72*
Grain or Forage Sorghum
1 post-emergence app
1.0 lb a.e./acre
10.41
0.72*
Non-Agricultural Uses
Non-cropland
1 app @ 4 lb a.e./acre
41.65
2.86*
Ornamental Turf
2 apps @ 1.5 lb
a.e./acre
(21-day interval)
15.62
1.07*
Grass Grown for Seed and
Sod
2 apps @ 2 lb a.e./acre
(21-day interval)
20.83
1.43*
Direct Application to Water Uses
Aquatic Weed Control
1 app @ 10.8 lb
a.e./acre foot
562.30
38.68*
Aquatic Weed Control
2 app @ 2 lb a.e./acre
(30-day interval)
20.83
1.43*
Aquatic Weed Control
2 app @ 4 lb a.e./acre
(21-day interval)
41.65
2.86*
1 EEC based on soil concentration.
Calculation based on rat acute oral dose LD50 =441mg a.e./kg-bw (MRID 414135-01).
*Acute RQ > 0.1 exceeds acute listed species level of concern (LOC).
5.1.2.2.2 Birds (Assessed for AW Only)
An additional prey item of the AW is small birds. In order to assess risks to these
organisms, dietary-based and dose-based exposures modeled in T-REX for a small bird
(20 g) consuming short grass are used for non-granular applications to estimate acute and
chronic risks (Table 5.8). Acute risks for granular applications are estimated in Table
5.6.a. Since the acute and chronic RQs are exceeded, there is a potential for indirect
effects to AW as they rely on avian prey during at least some portion of their life-cycle.
133
-------
T:ihlc5.8 I ppcr-hound Koiio«;i Nomogram Kl
Cs lor Diolsirv- iind Dosc-bnscd Kxposurcs of
(lie Torroslr
;il-ph;isc
CUI.K iind AW sinri its I'rcv lo Liquid Applic:ilions of 2.4-1)
HQs lor A\ inn Pro
(Indirect r.l'l'ecls to AW r
HQs lor TerreMrial
ln\crlchralc Piv\ (Indirecl
I'.ITecls lo CUM- and AW )
Modeling
Scenario
Melliod1
Application Kale
Anile
dose-based
(Small hud
consilium'.:
( hronic
dielan-
based
Small
Large
(ISird
ln\crlch rales
ln\erleb rales
short grass.)
short grass)
Orchard Uses
Nut
Orchards,
Pistachios
G
2 apps @ 2 lb a.e./acre
(30-day interval)
2.79*
0.55
0.57**
0.06**
Filberts
G
4 apps @ 0.5 lb a.e./acre
(30-day interval)
0.70*
0.14
0.15**
0.02
Grapes (all)
G
1 app @ 1.36 lb a.e./acre
1.73*
0.34
0.35**
0.04
Blueberries
G
2 apps @ 1.4 lb a.e./acre
(30-day interval)
1.95*
0.38
0.40**
0.05**
Stone and
Pome Fruits
G
2 apps @ 2 lb a.e./acre
(75-day interval)
2.55*
0.50
0.53**
0.06**
Citrus
A/G
1 app (Si 0.1 lb a.e./acre
0.13*
0.02
0.03
0.004
Agricultural - Food Crop
Uses
1 app @ 1.0 lb a.e./acre
March 15,
Field Corn,
Popcorn
A/G
1 app @ 0.5 lb a.e./acre
April 29,
1 app @ 1.5 lb a.e./acre
August 15
1.91*
0.37
0.39**
0.05**
1 app @ 1 lb a.e./acre
Sweet Corn
A/G
March 15,
1 app @ 0.5 lb a.e./acre
April 29
1.27*
0.25
0.26**
0.03
Potatoes
A/G
2 apps @ 0.07 lb a.e./acre
(10-day interval)
0.13*
0.03
0.03
0.004
Sugarcane
A/G
2 apps @ 2 lb a.e./acre
(20-day interval)
3.07*
0.60
0.63**
0.07**
Cereal Grains
A/G
1 post-emergence app @ 1.25
lb a.e./acre,
1 pre-harvest app @ 0.5 lb
a.e./acre
(90-day interval)
1.59*
0.31
0.33**
0.04
Grain or
Forage
Sorghum
A/G
1 post-emergence app @1.0
lb a.e./acre
1.27*
0.25
0.26**
0.03
Hops
A/G
3 apps @ 0.5 lb a.e./acre
(30-day interval)
0.70*
0.14
0.15**
0.02
Asparagus
A/G
2 apps @ 2 lb a.e./acre
(30-day interval)
2.79*
0.55
0.57**
0.06**
Fallowland
and Crop
Stubble
A/G
2 apps @ 2 lb a.e./acre
(30-day interval)
2.79*
0.55
0.57**
0.06**
134
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Table 5.8 I ppcr-boiind kenega Nomogram KIX s lor Dietary- and Dose-based Kxposurcs of
(lie Terreslrial-pliase ( KM- and AW and its Prev lo Liquid Applications of 2.4-1)
HQs lor A\ ian Pre\
(Indirect r.lTecls (o AW r
RQs lor l erreslrial
ln\erlehrale Pre\ (Indirecl
r.lTecls lo ( Kl.l 'and AW )
Modeling
Scenario
Melliod1
Application Kale
AciHc
dose-hased
(Small hud
aiiisiimiiiu
sIkhi urassi
Chronic
dielan-
hased
(ISinl
aiiisiimiim
sliori mass)
Small
ln\erlehrales
large
ln\erlehrales
Agricultural - Non-food Crop Uses
Established
Grass
Pastures,
Rangeland,
Perennial
Grassland
Not in
Agricultural
Production
G
2 apps @ 2 lb a.e./acre
(30-day interval)
2.79*
0.55
0.57**
0.06**
Non-agricultural Uses
Non-cropland
A/G
1 app @ 4 lb a.e./acre
5.09*
1.00+
1.05**
0.12**
Forestry
A/G
1 app @ 4 lb a.e./acre
5.09*
1.00+
1.05**
0.12**
Tree and
Brush
Control
A/G
1 app @ 4 lb a.e./acre
5.09*
1.00+
1.05**
0.12**
Ornamental
Turf
A/G
2 apps @ 1.5 lb a.e./acre
(21-day interval)
2.28*
0.45
0.47*
0.05**
Grass Grown
for Seed and
Sod
A/G
2 apps @ 2 lb a.e./acre
(21-day interval)
3.03*
0.59
0.63**
0.07**
Direct Application to Water Uses
Rice
A/G
1 app @ 1.5 lb a.e./acre
1.91*
0.37
0.39**
0.05**
Aquatic Weed
Control
A/G
1 app @ 10.8 lb a.e./acre foot3
68.75*
13.47+
14.16**
1.57**
Aquatic Weed
Control
A/G
2 app @ 2 lb a.e./acre
(30-day interval)
2.79*
0.55
0.57**
0.06**
Aquatic Weed
Control
A/G
2 app @ 4 lb a.e./acre
(21-day interval)
6.07*
1.19+
1.24**
0.14**
'G = ground application. A = aerial application.
2EECs based on small bird (20 g) which consumes short grass.
3Label states apply 10.8 lb a.e./acre-foot. If water body is 5 ft deep, this equals an application rate of 54 lb a.e/.acre
*Acute RQ >0.1 exceeds acute listed species level of concern (LOC) for birds.
**Acute RQ > 0.05 exceeds acute level of concern (LOC) for terrestrial invertebrates.
+Chronic RQ >1.0 exceeds chronic level of concern (LOC) for birds.
5.1.2.2.3 Terrestrial Invertebrates
In order to assess the risks of 2,4-D to terrestrial invertebrates, the honey bee is used as a
surrogate for terrestrial invertebrates. The toxicity value for terrestrial invertebrates is
135
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calculated by multiplying the lowest available acute contact LD50 of 66 |ig a.e./bee by 1
bee/0.128g, which is based on the weight of an adult honey bee. EECs (|ig a.e./g of bee)
calculated by T-REX for small and large insects are divided by the calculated toxicity
value for terrestrial invertebrates, which is 515 mg a.e./kg-insect. It is important to note
that the calculated RQs may overestimate risk as the LD50 values from all submitted bee
studies were non-definitive (50% mortality was not reached at the highest dose). The
results of the bee RQs are tabulated in Table 5.8.
Based on the bee RQ calculations, all of the modeled uses of 2,4-D except citrus and
potatoes exceed the LOC for acute risk to small terrestrial invertebrates with RQs ranging
from 0.15 to 14.16. For large invertebrates, all uses except filberts, grapes, citrus, sweet
corn, potatoes, cereal grains, grain or forage sorghum, and hops exceed the LOC with
RQs ranging between 0.05 to 1.57 (Table 5.8).
5.1.2.2.4 Frogs
An additional prey item of the adult terrestrial-phase CRLF and AW is other species of
frogs. In order to assess risks to these organisms, dietary-based and dose-based
exposures modeled in T-REX for a small bird (20 g) consuming small invertebrates are
used for non-granular applications to estimate acute and chronic risks. Acute and chronic
risks for liquid applications are estimated in Table 5.5, and acute risks for granular
applications are estimated in Table 5.6.a. These acute and chronic LOC exceedances
indicate that there is a potential for indirect effects to those listed species that rely on
birds (and, thus, reptiles and/or terrestrial-phase amphibians) during at least some portion
of their life-cycle {i.e., CRLF and AW).
5.1.2.3 Indirect Effects to Terrestrial-phase CRLF and AW via
Reduction in Terrestrial Plant Community (Riparian
and Upland Habitat)
Potential indirect effects to the CRLF resulting from direct effects on riparian and upland
vegetation are assessed using RQs from terrestrial plant seedling emergence and
vegetative vigor EC25 data as a screen. Based on the TerrPlant modeling results, there are
LOC exceedances for all modeled uses except for citrus and potatoes for risks to non-
listed monocot plants; all modeled uses result in LOC exceedances for all non-listed dicot
plants. RQs that exceed the LOC range from 2.63 to 22.68 for monocots and 2.98 to
183.33 for dicots (Tables 5.9.a and 5.9.b), Since the non-listed plant LOCs are exceeded,
there is potential for indirect effects to those listed species that rely on terrestrial plants
during at least some portion of their life-cycle {i.e., CRLF and AW).
136
-------
Tsihle 5.9.si I crrPhiiH KQs lor Monocols Inhnhilin
« Dry siihI Semi-siqusilic Aresis Kxposed lo 2.4-
1) \ i;i K11110IT mid Dril'l (single npplicnlion only)
Modeling
Melliod1
Application Kale
Dril'i
l)r\ Area
Semi-a(|iialic
Spra\ Drill
KQ
Scenario
Value (" <»)
RQ
Area RQ
Orchard Uses
Nut Orchards,
n
2 apps @ 2 lb a.e./acre
1
1.24*
10.52*
0.23
Pistachios
(30-day interval)
Filberts
G
4 apps @ 0.5 lb a.e./acre
(30-day interval)
1
0.31
2.63*
<0.1
Grapes (all)
G
1 app @ 1.36 lb a.e./acre
1
0.84
7.15*
0.15
Blueberries
G
2 apps @ 1.4 lb a.e./acre
(30-day interval)
1
0.87
7.36*
0.16
Stone and Pome
Fruits
G
2 apps @ 2 lb a.e./acre
(75-day interval)
1
1.24*
10.52*
0.23
Citrus
A
1 app @ 0.1 lb a.e./acre
0.10
0.57
<0.1
G
1
<0.1
0.53
<0.1
Agricultural - Food Crop Uses
1 app @ 1.0 lb a.e./acre
A
March 15,
Field Corn,
1 app @ 0.5 lb a.e./acre
5
1.55*
8.51*
0.85
Popcorn
G
April 29,
1 app @ 1.5 lb a.e./acre
August 15
1
0.93
7.89*
0.17
A
1 app @ 1 lb a.e./acre
March 15,
1 app @ 0.5 lb a.e./acre
April 29
5
1.03*
5.67*
0.57
Sweet Corn
G
1
0.62
5.26*
0.11
Potatoes
A
2 apps @ 0.07 lb a.e./acre
5
<0.1
0.40
<0.1
G
(10-day interval)
1
<0.1
0.37
<0.1
Sugarcane
A
2 apps @ 2 lb a.e./acre
5
2.06*
11.34*
1.14*
G
(20-day interval)
1
1.24*
10.52*
0.23
A
1 post-emergence app @ 1.25
Cereal Grains
lb a.e./acre,
5
1.29*
7.09*
0.71
G
1 pre-harvest app @ 0.5 lb
a.e./acre
(90-day interval)
1
0.77
6.57*
0.14
Grain or Forage
A
1 post-emergence app @ 1.0
5
1.03*
5.67*
0.57
Sorghum
G
lb a.e./acre
1
0.62
5.26*
0.11
Hops
A
3 apps @ 0.5 lb a.e./acre
5
0.52
2.84*
0.28
G
(30-day interval)
1
0.31
2.63*
<0.1
Asparagus
A
2 apps @ 2 lb a.e./acre
5
2.06*
11.34*
1.14*
G
(30-day interval)
1
1.24 *
10.52*
0.23
Fallowland and
A
2 apps @ 2 lb a.e./acre
5
2.06*
11.34*
1.14*
Crop Stubble
G
(30-day interval)
1
1.24 *
10.52*
0.23
Agricultural - Non-food Crop Uses
Established Grass
Pastures,
Rangeland,
Perennial
G
2 apps @ 2 lb a.e./acre
(30-day interval)
1
1.24*
10.52*
0.23
Grassland Not in
Agricultural
137
-------
Tsihlc 5.9.;i TcrrPhinl KQs lor Monocols Inhsihiling l)r\ siml Sonii-:i(|n:ilic Arcsis Kxposctl lo 2.4-
1) \ i;i KiiiioIT ;ind Drill (single sipplicsilion onlv)
Modeling
Scenario
Method1
Application Kale
Drill
\ alue i
Dn Area
HQ
Semi-a(|iialic
Area UO
Spra\ Drill
Production
Non-agricultural Uses
Non-cropland
A
1 app @ 4 lb a.e./acre
5
4.12*
22.68*
2.27*
G
1
2.47*
21.03*
0.45
Forestry
A
1 app @ 4 lb a.e./acre
5
4.12*
22.68*
2.27*
G
1
2.47*
21.03*
0.45
Tree and Brush
Control
A
1 app @ 4 lb a.e./acre
5
4.12*
22.68*
2.27*
G
1
2.47*
21.03*
0.45
Ornamental Turf
A
2 apps @ 1.5 lb a.e./acre
(21-day interval)
5
1.55*
8.51*
0.85
G
1
0.93
7.89*
0.17
Grass Grown for
Seed and Sod
A
2 apps @ 2 lb a.e./acre
(21-day interval)
5
2.06*
11.34*
1.14*
G
1
1.24*
10.52*
0.23
Direct Application to Water Uses
Rice
A
1 app @ 1.5 lb a.e./acre
5
1.55*
8.51*
0.85
G
1
0.93
7.89*
0.17
'G = ground application. A = aerial application. All applications are liquid unless otherwise specified.
2EECs calculated based on a single application. If crop labeled for multiple applications within a year, the highest single
rate was used.
*RQ >1.0 exceeds non-listed level of concern (LOC).
Tsihlc 5.9.h TcrrPhinl KQs lor Dieols Inhsihiling Dry ;iihI Scini-;i(|ii;ilie A reus Kxposcd lo 2.4-1)
visi KiiiioITiiiul Drill (single sipplicnlion onlv)
Modeling
Scenai'io
Method'
Application Kale
Drift
Value
Dn Area
HQ
Semi-a(|iialic
Area KQ
Spra\ Drill
HQ
Orchard Uses
Nut Orchards,
Pistachios
G
2 apps @ 2 lb a.e./acre
(30-day interval)
1
10.00*
85.00*
9.52*
Filberts
G
4 apps @ 0.5 lb a.e./acre
(30-day interval)
1
2.50*
21.25*
2.38*
Grapes (all)
G
1 app @ 1.36 lb a.e./acre
1
6.80*
57.80*
6.48*
Blueberries
G
2 apps @ 1.4 lb a.e./acre
(30-day interval)
1
7.00*
59.50*
6.67*
Stone and Pome
Fruits
G
2 apps @ 2 lb a.e./acre
(75-day interval)
1
10.00 *
85.00*
9.52*
138
-------
Tsihlc 5.9.h TcrrPhinl UQs lor Diools lnhnhilin Uses
Established
Grass Pastures,
Rangeland,
Perennial
Grassland Not
in Agricultural
Production
G
2 apps @ 2 lb a.e./acre
(30-day interval)
1
10.00 *
85.00*
9.52*
Non-agricultural Uses
139
-------
Table 5.9.b TerrPlanl KQs lor Dicols Inhabiting l)rv and Semi-aqiialic Areas Kxposed lo 2.4-1)
via UiinolTand Drift (single application only)
Modeling
Seen ;i rio
Method1
Application Kale
Drill
Value CM.)
Dn Area
HO
Semi-a(|iialic
Area UO
Spra\ Drill
RQ
Non-cropland
A
1 app @ 4 lb a.e./acre
5
33.33*
183.33*
95.24*
G
1
20.00*
170.00*
19.05*
Forestry
A
1 app @ 4 lb a.e./acre
5
33.33*
183.33*
95.24*
G
1
20.00*
170.00*
19.05*
Tree and Brush
Control
A
1 app @ 4 lb a.e./acre
5
33.33*
183.33*
95.24*
G
1
20.00*
170.00*
19.05*
Ornamental
Turf
A
2 apps @ 1.5 lb a.e./acre
(21-day interval)
5
12.50*
68.75*
35.71*
G
1
7.50*
63.75*
7.14*
Grass Grown
for Seed and
Sod
A
2 apps @ 2 lb a.e./acre
(21-day interval)
5
16.67
91.67*
47.62*
G
1
10.00*
85.00*
9.52*
Direct Application to Water Uses
Rice
A
1 app @ 1.5 lb a.e./acre
5
12.50*
68.75*
35.71*
G
1
7.50*
63.75*
7.14*
'G = ground application. A = aerial application. All applications are liquid unless otherwise specified.
2EECs calculated based on a single application. If crop labeled for multiple applications within a year, the highest single
rate was used.
*RQ >1.0 exceeds non-listed level of concern (LOC).
5.1.3 Primary Constituent Elements of Designated Critical Habitat
For 2,4-D use, the assessment endpoints for designated critical habitat PCEs involve the
same endpoints as those being assessed relative to the potential for direct and indirect
effects to the listed species assessed here. Therefore, the effects determinations for direct
and indirect effects are used as the basis of the effects determination for potential
modification to designated critical habitat. The potential for effects on critical habitat
PCEs are discussed in Section 5.2.4,
5.2 Risk Description
The risk description synthesizes an overall conclusion regarding the likelihood of adverse
impacts leading to an effects determination {i.e., "no effect," "may affect but not likely to
adversely affect," or "may affect and likely to adversely affect") for the CRLF and the
AW and their designated critical habitats. If the RQs presented in the Risk Estimation
(Section 5.1) show no direct or indirect effects for the assessed species, and no
140
-------
modification to PCEs of the designated critical habitat, a "no effect" determination is
made, based on 2,4-D's use within the action area. However, if LOCs for direct or
indirect effect are exceeded or effects may modify the PCEs of the critical habitat, the
Agency concludes a preliminary "may affect" determination for the FIFRA regulatory
action regarding 2,4-D.
Based on the RQ results from the direct and indirect risk estimation for 2,4 D, a
preliminary effects determination for the CRLF and the AW is "may affect." A summary
of the risk estimation results are provided in Table 5.10.a and 5.11.a for direct and
indirect effects to the listed species assessed here and in Table 5.10.b and 5.11.b for the
PCEs of their designated critical habitat.
Table 5.IO.a Risk l.slimalion Summary lor 2.4-1) - Direct and Indirect KITecls to ( Kl.l-
I.OC
r.\ceedances
(Y/N)
Description of Results of Risk I'lslimalion
(i
Aquatic Phase
'^s, larvae, tadpoles, juveniles, and adults)
Direct Effects
Survival, growth, and reproduction of
CRLF individuals via direct effects on
aquatic phases.
Yes
Survival: LOC was exceeded in the aerial Forestry, Tree and
Brush Control runoff and drift ester uses and all direct
application to water scenarios (Table 5.1.a, 5.1.b, and 5.1.c).
Growth and reproduction: Chronic LOC was not exceeded for
any scenarios (Table 5.1.a and 5.1.b).
Indirect Effects
Survival, growth, and reproduction of
CRLF individuals via effects to food
supply (i.e., freshwater invertebrates,
non-vascular plants).
Yes
Freshwater fish: Listed Species LOC was exceeded in the
aerial Forestry, Tree and Brush Control runoff and drift ester
uses and all direct application to water scenarios, no Chronic
LOCs exceeded (Table 5.1.a, 5.1.b, and 5.1.c).
Non-vascular aquatic plants: LOC was exceeded for all direct
surface aquatic weed control scenarios (Table 5.2).
Freshwater invertebrates'. Acute LOC was exceeded for all
direct application to water scenarios (Table 5.3.a and 5.3.b).
Indirect Effects
Survival, growth, and reproduction of
CRLF individuals via effects on
habitat, cover, and/or primary
productivity (i.e., aquatic plant
community).
Yes
Non-vascular aquatic plants: LOC was exceeded for all direct
surface aquatic weed control scenarios (Table 5.2).
Vascular aquatic plants: LOC was exceeded for several
acid/salt use scenarios and all direct application to water
scenarios (Table 5.4.a and 5.4.b).
Indirect Effects
Survival, growth, and reproduction of
CRLF individuals via effects to
riparian vegetation, required to
maintain acceptable water quality and
habitat in ponds and streams
comprising the species' current range.
Yes
Terrestrial plants: LOCs were exceeded for monocots for all
modeled scenarios except citrus and potatoes. LOCs were
exceeded for dicots for all modeled scenarios. (Tables 5.9.a
and 5.9.b).
I'er rest rial Phase
(Juveniles and adults)
141
-------
Tsihle 5.IO.;i Kisk l.sliinnlion Suininnrv lor 2.4-1) - Direct :iihI Indirect KITccIs 1» CUM''
I.OC
r.\ccedances
(Y/N)
Description of Results of Kisk 1'stim;i 1 ion
Direct Effects
Survival, growth, and reproduction of
CRLF individuals via direct effects on
terrestrial phase adults and juveniles.
Yes
Survival: Acute LOC was exceeded in all modeled scenarios
except citrus and potatoes for liquid applications. Acute LOC
was exceeded in non-cropland, ornamental turf, grass grown
for sod and all direct water application scenarios (ditchbanks)
for granular applications (Tables 5.5,5.6.a, and 5.6.b).
Growth and reproduction: Dietary-based chronic RQ values
exceeded the LOC at 1 app @ 54 lb a.e./acre for aquatic weed
control (ditchbanks) for liquid application (Table 5.5).
Indirect Effects
Survival, growth, and reproduction of
CRLF individuals via effects on prey
(i.e., terrestrial invertebrates, small
terrestrial mammals and terrestrial
phase amphibians).
Yes
Terrestrial invertebrates: Acute LOC for small insects was
exceeded for all scenarios except citrus and potatoes. Acute
LOC for large insects was exceeded for several scenarios.
(Table 5.8).
Terrestrial-phase amphibians'. Acute LOCs were exceeded in
all T-REX modeled scenarios except citrus and potatoes for
liquid applications. Acute LOC was exceeded in non-cropland,
ornamental turf, grass grown for sod and all direct water
application scenarios (ditchbanks) for T-REX modeled granular
applications (Table 5.5 and 5.6.a).
Small terrestrial mammals'. Acute LOC was exceeded in all
modeled scenarios except citrus and potatoes for liquid
applications. Acute LOC was exceeded in non-cropland,
ornamental turf, grass grown for sod and all direct water
application scenarios (ditchbanks) for granular applications
(Table 5.5 and 5.7).
Indirect Effects
Survival, growth, and reproduction of
CRLF individuals via effects on habitat
(i.e., riparian vegetation).
Yes
Terrestrial plants: LOCs were exceeded for monocots for all
modeled scenarios except citrus and potatoes. LOCs were
exceeded for dicots for all modeled scenarios (Tables 5.9.a
and 5.9.b).
142
-------
Tsihlc 5.10.1) Kisk l.sliinnlion Suinninrv lor 2.4-1) - I'CT.s of l)osi»ii;Ho(l (rilienl 11 ;ihit;i 1 lor (lie
CUM'"1
Assessment r.ndpoinl
1 l;il)il;il
Mn(lirii;iiiiin
-------
Tsihlc 5.10.1) Uisk Kslimsilion Suniinnrv lor 2.4-1) - I'CT.s of Designated (rilicnl Ihihilsil lor (lie
CUM'"1
Assessment l.ndpoinl
1 liil)il;il
Mii(lirk;ilii>n
-------
Table 5.1 l.n Kisk l.slimnlion Suininnrv lor 2.4-1) - Direct sind Indirect KITeds lo (lie AW
Assessment l.ndpoinl
Habitat
Modification
(Y/N)
Description of Results of Kisk I'lstimalion
Indirect Effects
Survival, growth, and reproduction
of AW individuals via effects on
prey (i.e., terrestrial invertebrates,
small terrestrial mammals and
terrestrial phase amphibians).
Yes
Terrestrial invertebrates: Acute LOC for small insects was
exceeded for all scenarios except citrus and potatoes. Acute
LOC for large insects was exceeded for several scenarios.
(Table 5.8).
Terrestrial-phase amphibians'. Acute LOCs were exceeded in
all T-REX modeled scenarios except citrus and potatoes for
liquid applications. Acute LOC was exceeded in non-cropland,
ornamental turf, grass grown for sod and all direct water
application scenarios (ditchbanks) for T-REX modeled granular
applications (Table 5.5 and 5.6.a).
Small terrestrial mammals'. Acute LOC was exceeded in all
modeled scenarios except citrus and potatoes for liquid
applications. Acute LOC was exceeded in non-cropland,
ornamental turf, grass grown for sod and all direct water
application scenarios (ditchbanks) for granular applications
(Table 5.5 and 5.7).
Small birds: Acute LOC exceeded in all modeled scenarios
(Table 5.6a and 5.8).
Indirect Effects
Survival, growth, and reproduction
of AW individuals via effects on
habitat (i.e., riparian vegetation).
Yes
Terrestrial plants: LOCs were exceeded for monocots for all
modeled scenarios except citrus and potatoes. LOCs were
exceeded for dicots for all modeled scenarios (Tables 5.9.a
and 5.9.b).
145
-------
Tsihlc 5.1 l.h Kisk l.slimnlion Suinninrv lor 2.4-1) - I'CT.s of Designated ( rilienl 11 ;ihit;i 1 lor (lie
AW1
!.()(
-------
¦ Harm includes significant habitat modification or degradation that results
in death or injury to listed species by significantly impairing behavioral
patterns such as breeding, feeding, or sheltering.
¦ Harass is defined as actions that create the likelihood of injury to listed
species to such an extent as to significantly disrupt normal behavior
patterns which include, but are not limited to, breeding, feeding, or
sheltering.
Likelihood of the Effect Occurring: Discountable effects are those that are
extremely unlikely to occur.
Adverse Nature of Effect: Effects that are wholly beneficial without any adverse
effects are not considered adverse.
A description of the risk and effects determination for each of the established assessment
endpoints for the CRLF and the AW and their designated critical habitats is provided in
Sections 5.2.1 through 5.2.3,
As previously discussed, the results of this analysis lead to a preliminary "may affect"
determination for the CRLF and the AW based on labeled 2,4-D usage in California due
to the large number of LOC exceedances across multiple taxonomic groups and multiple
cropping scenarios.
For both the CRLF and the AW, this "may affect" determination is refined to a "likely to
adversely affect" (LAA) determination for all labeled crops except citrus and potatoes
based on the characterization of potential effects and likelihood of exposure discussed
below. Citrus and potato 2,4-D use is refined to a "may affect, not likely to adversely
affect" (NLAA) determination.
5.2.1 Direct Effects
5.2.1.1 Aquatic-Phase CRLF
The aquatic-phase considers life stages of the frog that are obligatory aquatic organisms,
including eggs and larvae. It also considers submerged terrestrial-phase juveniles and
adults, which spend a portion of their time in water bodies that may receive runoff and
spray drift containing 2,4-D.
LOC exceedances:
Of the scenarios modeled, acute listed species LOCs were exceeded in the aerial Forestry
and Tree and Brush Control uses as well as all of the direct application to water uses
(Rice and Aquatic Weed Control). Exceeding RQs ranged from 0.05 to 15.38. There were
no chronic LOC exceedances.
Comparison of modeled to observed water concentrations:
The available monitoring data were presented in Section 3.2.7, Compared with the
modeling results, the modeled values are much higher than USGS NAWQA and CDPR
data for California. The lack of agreement between the model and monitoring results is
147
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not unexpected since the monitoring data were not designed to target areas of 2,4-D
usage. With the exception of direct aquatic applications such as rice use and aquatic weed
control, the model predictions are comparable with the available registrant-submitted fate
studies.
Analysis of aquatic-phase amphibian data:
As previously discussed in the aquatic toxicity portion of this assessment (Section 4.2),
aquatic amphibian data were submitted by the registrant and available in the open
literature. However, since it was less sensitive than the freshwater fish data and it is
unknown where the CRLF falls on sensitivity distribution for aquatic-phase amphibians
or on a sensitivity distribution for aquatic invertebrates, EFED determined that using the
most sensitive aquatic vertebrate toxicity data would be appropriate. However, even if the
reviewed frog data were used to calculate RQs, there Listed Species LOC would still be
exceeded (Table 5.12). The most sensitive amphibian toxicity values for acid/ salt
(Western chorus frog tadpoles LC50 =181 mg a.e./L, E61180) and ester (Leopard frog
tadpoles LC50 = 0.5 05 mg a.e./L, MRLD 445173-05) are used to calculate RQs. The
LOCs for ester direct application to water scenarios would still be exceeded with RQs
ranging from 1.5 to 7.9; however, the LOC is no longer exceeded for acid/salt direct
application to water scenarios, rice applications (RQ = 0.008), or for the Forestry/Tree
and Brush Control (ester drift+runoff, aerial) scenario (RQ = 0.04).
Table 5.12 Acute KQs lor amphibians and KIX's lor direct application to water to represent 2.4-1) acid,
salt, and ester uses (based 011 the most sensitive amphibian toxicity data)
Master l.ahcl I so
Model Scenario
Method1
Application Kale
Peak
I.I.C
Acute RQ1
(iiii/l.l
Acid/salt
r.sler
Aqualic \\ ccd Control
(surface application or
subsurface injection)
Direct water
applications
G & A
10.8 lb a.e./acre-ft
(to achieve 4 ppm
concentration)
40002
0.02
7.9*
Aquatic Weed Control
Direct water
applications
G & A
2 app @2 lb a.e./acre
(30-day interval)
740
0.004
1.5*
Aquatic Weed Control
Direct water
applications
G & A
2 app @ 4 lb a.e./ acre
(21-day interval)
1480
0.008
2.9*
*LOC exceedances (acute RQ > 0.05 are bolded; Acute RQ (acid and salts) = use-specific peak EEC /181 mg a.e./L (E61180
western chorus frog tadpole). Acute RQ (esters) = use-specific peak EEC / 0.505 mg a.e./L (MRID 445173-05 leopard frog tadpole).
'G = ground application. A = aerial application.
2Aquatic weed control-peak water concentration: 4000 |ig/L , For ester direct application scenarios, 2,4-D acid input parameters were
used to determine EEC. All other runoff and drift application scenarios used 2,4-D ester input parameters to determine the EEC.
148
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5.2.1.2
Terrestrial-Phase CRLF and AW
The terrestrial-phase of the CRLF considers juvenile and adult life stages during which
much time is spent in a terrestrial habitat. Submerged terrestrial-phase CRLFs are not
considered here; their exposure is addressed as an aquatic-phase CRLF. Life history for
the AW states that it is an obligatory terrestrial organism. Since no toxicity data were
available for terrestrial-phase amphibians or reptiles, toxicity data for birds were used a
surrogate.
LOC exceedances:
All the 2,4-D modeled uses except Citrus and Potatoes have the potential to directly
affect the CRLF and AW based on the acute LOC exceedances demonstrated in T-REX.
Based on T-REX, the only use with chronic direct effect concerns is aquatic weed control
via surface application.
T-HERPS refinements:
Because the above risk estimation identified LOC exceedances for the terrestrial-phase
CRLF and the AW, the T-HERPS model was used as a standard protocol for further
refining the assessment for direct effects to the CRLF and the AW. T-HERPS was used to
refine acute dose-based, chronic-dietary, and sub-acute dietary risks to the terrestrial-
phase CRLF and AW via consumption of large insects, small herbivorous mammals,
small insectivorous mammals, and small terrestrial-phase amphibians exposed to liquid
applications already identified by T-REX. Dose-based acute RQs exceeding Listed
Species LOCs ranged from 0.28-2.01(Tables 5.13.a to 5.13.c), and dietary-based chronic
RQs exceeding Chronic LOC ranged from 7.58-8.88 (Table 5.13.d), Based on the results
of the T-HERPS model, all the modeled uses except uses on potato and citrus resulted in
LOC exceedances, although there were fewer exceedances for smaller organisms (14 g)
than there were for larger organisms (238 g).
149
-------
Tsihlc 5.13.21 Siiiiiinsirv of T-III-IUPS Tcrrcstrisil-Phsisc Amphihinn l)osc-h;iscd UQ Kxcccdsinccs
lor Direct K fleets lo (lie (smsill. 14 g) CUM'' nnd AW IVoin Ingestion of Residues on or in Prev
Items (linsed on Liquid Applications <»l'2.4-1))
Modeling
Method1
Application Kale
l-ood hem
Small (14 »)
Scenario
Dose-hased
I I.( (ppni)
Dose-hased
Acule UQ
Direct water application use
Aquatic Weed
A/G
1 app @ 10.8 lb
Broadleaf plants and small
insects
283.23
0.95
Control
a.e./acre foot2
Fruits/pods/seeds and large
insects
31.47
0.11
'G = ground application. A = aerial application.
2Label states apply 10.8 lb a.e./acre-foot. If water body is 5 ft deep, this equals an application rate of 54 lb a.e/.acre
*A11 bolded values exceed Level of Concern (LOC) for the following risk categories:
Acute Risk to Herpetofauna Dietary items 0.5
Herpetofauna Dietary items for Acute Restricted Use 0.2
Acute Listed Species of Herpetofauna Dietary items 0.1
Tsihlc 5.13.1) Snin 111:1 r\ ol"
-IIKUPS Tcrrcstrisil-Phsisc Amphihisin l)osc-h:iscd UQ V.
vcccdsinccs
lor Direct K fleets to the (medium. 37 «) ( KM- nnd AW IVoin Ingestion ol' Ucsiducs on or in I'rcv
Items (lisiscd on 1
iquid Applications <»l'2.4-1))
Medium (J"7»)
Modeling Scenai'io
Method1
Applicalion Kale
l-ood liem
Dose-based
l-'.l-'.C (ppni
Dose-based
Acule KQ
Orchard Uses
Nut Orchards,
Pistachios
G
2 apps @ 2 lb a.e./acre
(30-day interval)
Small herbivore mammals
327.36
1.10
Filberts
G
4 apps @ 0.5 lb a.e./acre
(30-day interval)
Small herbivore mammals
82.57
0.28
Grapes (all)
G
1 app @ 1.36 lb a.e./acre
Small herbivore mammals
203.45
0.68
Blueberries
G
2 apps @ 1.4 lb a.e./acre
(30-day interval)
Small herbivore mammals
229.15
0.77
Stone and Pome
Fruits
G
2 apps @ 2 lb a.e./acre
(75-day interval)
Small herbivore mammals
300.01
1.01
Agricultural - Food Crop Uses
150
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Table 5.13.1) Siiiniiiiirv of T-IIKUPS Torroslrisd-Phsiso Amphibian Dosc-bnscd UQ KxccodsiiUTs
lor Direct KITccls 1» (lie (medium. 37 «) ( KM- and AW IVoni Ingestion of Residues on or in Prcv
Items (linsed on Liquid Applications <»l'2.4-1))
Medium (J"7«)
Modelinii Scenario
Mclhod1
Applicalion Kale
l-ood lli'in
Dose-based
I I.( (ppni)
Dose-based
Acule UQ
1 app @ 1.0 lb a.e./acre
March 15,
Field Corn, Popcorn
A/G
1 app @ 0.5 lb a.e./acre
April 29,
1 app @ 1.5 lb a.e./acre
August 15
Small herbivore mammals
230.88
0.77
1 app @ 1 lb a.e./acre
Sweet Corn
A/G
March 15,
1 app @ 0.5 lb a.e./acre
April 29
Small herbivore mammals
149.60
0.50
Sugarcane
A/G
2 apps @ 2 lb a.e./acre
(20-day interval)
Small herbivore mammals
361.11
1.21
Cereal Grains
A/G
1 post-emergence app @
1.25 lb a.e./acre,
1 pre-harvest app @ 0.5 lb
a.e./acre
(90-day interval)
Small herbivore mammals
187.00
0.63
Grain or Forage
Sorghum
A/G
1 post-emergence app @
1.0 lb a.e./acre
Small herbivore mammals
149.60
0.50
Hops
A/G
3 apps @ 0.5 lb a.e./acre
(30-day interval)
Small herbivore mammals
82.50
0.28
Asparagus
A/G
2 apps @ 2 lb a.e./acre
(30-day interval)
Small herbivore mammals
327.36
1.10
Fallowland and
Crop Stubble
A/G
2 apps @ 2 lb a.e./acre
(30-day interval)
Small herbivore mammals
327.36
1.10
Agricultural - Non-food Crop Uses
Established Grass
Pastures,
Rangeland,
Perennial Grassland
Not in Agricultural
Production
G
2 apps @ 2 lb a.e./acre
(30-day interval)
Small herbivore mammals
327.36
1.10
Non-agricultural Uses
Small herbivore mammals
598.39
2.01
Non-cropland
A/G
1 app @ 4 lb a.e./acre
Small insectivore
mammals
37.40
0.13
Small herbivore mammals
598.39
2.01
Forestry
A/G
1 app @ 4 lb a.e./acre
Small insectivore
mammals
37.40
0.13
Tree and Brush
A/G
1 app @ 4 lb a.e./acre
Small herbivore mammals
598.39
2.01
Control
Small insectivore
37.40
0.13
151
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Table 5.13.1) Siiiniiiiirv of T-IIKUPS Terreslrisd-I'hsise Amphibian Dose-based UQ Kxoeedanoes
lor Direct KITeols 1» (lie (medium. 37 «) ( KM- and AW IVoni Ingestion of Residues on or in Prev
Items (liased on Liquid Applications <»l'2.4-1))
Medium (J"7«)
Modelinii Scenario
Method1
Application Kale
l-ood Id'iii
Dose-hased
I I.( (ppni)
Dose-hased
Acule UQ
mammals
Ornamental Turf
A/G
2 apps @ 1.5 lb a.e./acre
(21-day interval)
Small herbivore mammals
267.32
0.90
Grass Grown for
Seed and Sod
A/G
2 apps @ 2 lb a.e./acre
(21-day interval)
Small herbivore mammals
356.42
1.20
Direct Application to Water Uses
Rice
A/G
1 app @ 1.5 lb a.e./acre
Small herbivore mammals
224.40
0.75
Small herbivore mammals
8078.29
27.11
Aquatic Weed
Control
A/G
1 app @ 10.8 lb a.e./acre
foot2
Small insectivore
mammals
504.89
1.69
Broadleaf plants and
small insects
278.35
0.93
Fruits/pods /seeds and
large insects
30.93
0.10
Aquatic Weed
Control
A/G
2 app @ 2 lb a.e./acre
(30-day interval)
Small herbivore mammals
327.36
1.10
Aquatic Weed
Control
A/G
2 app @ 4 lb a.e./acre
(21-day interval)
Small herbivore mammals
712.84
2.39
Small insectivore
mammals
44.55
0.15
'G = ground application. A = aerial application.
2 Label states apply 10.8 lb a.e./acre-foot. If water body is 5 ft deep, this equals an application rate of 54 lb a.e/.acre
*A11 bolded values exceed Level of Concern (LOC) for the following risk categories:
Acute Risk to Herpetofauna Dietary items 0.5
Herpetofauna Dietary items for Acute Restricted Use 0.2
Acute Listed Species of Herpetofauna Dietary items 0.1
152
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Tsihle 5.13.0 Sn in in ;i r\ of T-IILUPS Tcrreslrisil-Phsiso Aniphihinn Dosc-hnsotl KQ Lxeoedsineos
lor Direct LITocls 1» (lie (hirgc. 238 «) CUM'' nnd AW IVoin Ingestion of Residues on or in Prcv
Items (linscd on Liquid Applicsilions <»l'2.4-1))
m . i .i:.... i. .... i» 1:
Large(23S g)
tll'IMMII
. 11111IV <11 HH1 i\
-------
Table 5.13.0 Snin 111:1 r\ ol'T-IIKUPS Terreslrisd-Phsise Amphibian Dose-based KQ Kxeeedanees
lor Direct KITeels l» (lie (large. 238 «) CUM'' and AW IVoni Ingestion of Residues on or in Prey
Items (liased 011 Liquid Applications <»l'2.4-1))
l.ar»e (23S »)
Modeling Scenario
Method1
Application Kale
l-ood hem
Dose-hased
I I.( (ppni)
Dose-hased
Acme UO
Grass Grown for
Seed and Sod
A/G
2 apps @ 2 lb a.e./acre
(21-day interval)
Small herbivore mammals
55.41
0.19
Direct Application to Water Uses
Rice
A/G
1 app @ 1.5 lb a.e./acre
Small herbivore mammals
34.89
0.12
Aquatic Weed
1 app @ 10.8 lb a.e./acre
Small herbivore mammals
1255.87
4.21
A/G
Small insectivore mammals
78.49
0.26
Control
foot
Broadleaf plants and small
insects
182.43
0.61
Aquatic Weed
Control
A/G
2 app @ 2 lb a.e./acre
(30-day interval)
Small herbivore mammals
50.89
0.17
Aquatic Weed
Control
A/G
2 app @ 4 lb a.e./acre
(21-day interval
Small herbivore mammals
110.82
0.37
'G = ground application. A = aerial application.
2 Label states apply 10.8 lb a.e./acre-foot. If water body is 5 ft deep, this equals an application rate of 54 lb a.e/.acre.
*A11 bolded values exceed Level of Concern (LOC) for the following risk categories:
Acute Risk to Herpetofauna Dietary items 0.5
Herpetofauna Dietary items for Acute Restricted Use 0.2
Acute Listed Species of Herpetofauna Dietary items 0.1
154
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Table 5.l3.d Summary of T-IIKUPS Terrestrial-Phase Amphibian Dietary-based UQ
Kxcecdances for Direct Kfl'ects lo the ( KM- and AW from Ingestion of Residues on or in Prey
Items (liascd on Liquid Applications of 2.4-D)
Modeling Scenario
Mclliod1
Application Kale
Food hem
Dielan-
hased l i t
ippm)
Dielan-hased
Chronic UQ
Direct Application to Water Uses
Aquatic Weed
Control
A/G
1 app @ 10.8 lb a.e./acre
foot2
Small herbivore mammals
8539.90
8.88
Broadleaf plants and small
insects
7290.00
7.58
'G = ground application. A = aerial application.
2Label states apply 10.8 lb a.e./acre-foot. If water body is 5 ft deep, this equals an application rate of 54 lb a.e/.acre.
*A11 bolded values exceed Level of Concern (LOC) for the following risk categories:
Chronic Risk to Herpetofauna Dietary items 1
5.2.2 Indirect Effects (via Reductions in Prey Base)
5.2.2.1 Algae (Non-vascular Plants)
As discussed in Section 2.5.3, the diet of CRLF tadpoles is composed primarily of
unicellular aquatic plants {i.e., algae and diatoms) and detritus.
LOC exceedances:
LOCs were exceeded for the direct application to water aquatic weed control scenarios.
For acid/salt aquatic weed control uses, the RQ was 1.03. For ester aquatic weed control
uses, the RQ was 60.61.
Comparison of modeled to observed water concentrations:
The available monitoring data have been presented in Section 3.2.7, Compared with the
modeling results, the modeled values are much higher than USGS NAWQA and CDPR
data for California. The lack of agreement between the model and monitoring results is
not unexpected since the monitoring data were not designed to target areas of 2,4-D
usage. With the exception of direct aquatic applications, such as rice use and aquatic
weed control, the model predictions are comparable with the available registrant-
submitted fate studies.
5.2.2.2 Aquatic Invertebrates
The potential for 2,4-D to elicit indirect effects to the CRLF via effects on freshwater
invertebrate food items is dependent on several factors including: (1) the potential
magnitude of effect on freshwater invertebrate individuals and populations; and (2) the
number of prey species potentially affected relative to the expected number of species
155
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needed to maintain the dietary needs of the CRLF. Together, these data provide a basis
to evaluate whether the number of individuals within a prey species is likely to be
reduced such that it may indirectly affect the CRLF.
LOC exceedances:
Acute LOC exceedances were observed in the direct application to water scenarios. For
rice, the RQ was 0.06. For the acid/salt aquatic weed control use, the RQ was 0.16. For
the ester aquatic weed control use, the RQ was 1.82. There were no chronic exceedances.
Comparison of modeled to observed water concentrations:
The available monitoring data have been presented in Section 3.2.7, Compared with the
modeling results, the modeled values are much higher than USGS NAWQA and CDPR
data for California. The lack of agreement between the model and monitoring results is
not unexpected since the monitoring data were not designed to target areas of 2,4-D
usage. With the exception of direct aquatic applications, such as rice use and aquatic
weed control, the model predictions are comparable with the available registrant-
submitted fate studies.
5.2.2.3 Fish and Aquatic-phase Frogs
Evidence for indirect effects to fish and frogs as food items is the same as presented the
direct effects analysis for aquatic-phase CRLFs (Section 5.2.1.1),
5.2.2.4 Mammals
Life history data for terrestrial-phase CRLFs and AW indicate that large adult frogs and
AW consume small mammals.
LOC exceedances:
Acute dose-based RQs for all liquid and granular applications of 2,4-D except Citrus and
Potato exceeded the LOCs for small mammalian prey items.
Chronic RQ values representing 2,4-D exposures to small mammals indicate risks
resulting from some application scenarios. Dose-based chronic RQs exceeded the LOC
for all liquid applications. Dietary-based chronic RQ exceeded the LOC for liquid
applications of 4 applications @ 0.5 lb a.e./acre and greater.
Percent effect analysis:
A percent effect analysis was conducted by determining an expected percent effect on the
prey item (small mammals) at the RQ, implying effect at the calculated EEC. The percent
effect ranged from 0.003% to 100% depending on cropping scenario (Table 5.14).
156
-------
Citrus and Potatoes
Although the mammalian dose-based chronic LOC was exceeded for both the CRLF and
the AW prey, EFED determined that this effect would be insignificant as the potential
small effect on mammal reproduction (as prey of the CRLF and AW) would not likely
impact the overall prey base. It is anticipated that any effects would be small since the
RQs only mildly exceeded the LOC.
5.2.2.5 Birds (assessed for AW only)
Life history data for the AW indicates that AWs consume small birds.
LOC exceedances:
RQ values, estimated using T-REX, representing direct exposures of 2,4-D to the AW are
used to represent risks of 2,4-D to small birds in terrestrial habitats. The indirect effects
to birds as food items are based on the direct effects analysis for the AW (Section
5.2.1.2),
Percent effect analysis:
A percent effect analysis was conducted by determining an expected percent effect on the
prey item (small birds) at the RQ, implying effect at the calculated EEC. The percent
effect ranged from 0.003% to 100% depending on cropping scenario (Table 5.14).
Citrus and Potatoes
Although the avian acute dose-based LOC was exceeded for AW prey, EFED determined
that this effect was discountable and insignificant as the predicted percentage of acute
effect was only 0.0033% of the bird population (birds as prey items of the AW), and if
even if this effect did occur, the overall prey base of the AW would likely not be affected.
Table 5.14 Summary of Indirect KITecl UQs lor (lie Tcrrcslrial-pliasc ( KI.I- and AW
Probabilities
Percenl KITecl
Indirect elTecls (o ( KI.I-" and AW
Indirccl elTecls In AW
Masler Label I so ( aleiion
Mi*Jicsl - Dose-
based RQ lor
Mammals 1
Percent I'.ITed for
Mam mals :
Ili'Jiesl
Dose-based UQ
for Birds 1
Percenl I'.ITocl
lor Birds :
Orchard Uses
Nut Orchards, Pistachios
0.52
10%
2.79
98%
Filberts
0.13
0.003%
0.70
24%
Grapes (all)
0.32
1%
1.73
86%
Blueberries
0.36
2%
1.95
90%
Stone and Pome Fruits
0.47
7%
2.55
97%
Citrus
No LOC exceedance
N/A
0.13
0.0033%
Agricultural - Food Crop Uses
Field Corn, Popcorn
0.72(G)
26%
2.43(G)
96%
Sweet Corn
0.72(G)
26%
2.43(G)
96%
157
-------
Table 5.14 Summary of Imliret
Probabilities
1 KITecl UQs lor (lie Terreslrial-pliase CUM'" and AW . Percent KITecl
Indirccl cITccls (o CRI.F and AW
Indirccl cITecls lo AW
Maslcr Label I sc ( alcgon
llighesl - Dose-
based RQ lor
Mammals 1
Perccnl r.l'l'ecl for
Mammals :
llighesl
Dose-based UQ
for liirds 1
Perccnl F.ITecI
for liirds :
Potatoes
No LUC c\v_wdjiiv_v
\.A
0.13
0.0033%
Sugarcane
0.57
14%
3.07
99%
Cereal Grains
0.30
0.9%
1.59
82%
Grain or Forage Sorghum
0.72(G)
26%
2.43(G)
96%
Hops
0.13
0.003%
0.70
24%
Asparagus
0.52
10%
2.79
98%
Fallowland and Crop Stubble
0.52
10%
2.79
98%
Agricultural - Non-food Crop Uses
Established Grass Pastures,
Rangeland, Perennial Grassland
Not in Agricultural Production
0.52
10%
2.79
98%
Non-agricultural Uses
Non-cropland
2.86 (G)
98%
9.70 (G)
100%
Forestry
0.94
45%
5.09
100%
Tree and Brush Control
0.94
45%
5.09
100%
Ornamental Turf
1.07G)
55%
3.64(G)
99%
Grass Grown for Seed and Sod
1.43 (G)
76%
4.85 (G)
100%
Direct Application to Water Uses
Aquatic Weed Control
Ditchbank
1.43 (G)
76%
4.85 (G)
100%
Aquatic Weed Control
Surface application
2.86 (G)
98%
9.70 (G)
100%
Aquatic Weed Control
Surface application or subsurface
injection
38.68 (G)
100%
130.96 (G)
100%
'G = granular application. All other applications are liquid.
2A slope value was not available for the acute bird of LD50 298 mg a.e./kg-bw (MRID 442757-0) and mammals of LD50 441
mg a.e./kg -bw (MRID 414135-01), therefore the probability was calculated based on the default slope value of 4.5.
Confidence intervals (2,9)
5.2.2.6 Terrestrial Invertebrates
When the terrestrial-phase CRLF reaches juvenile and adult stages, its diet is mainly
composed of terrestrial invertebrates. Life history data for the AW state that the diet of
158
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the AW also includes invertebrates and may depend on an individual's size, sex, age, and
location. As previously discussed in Section 5.1.2.1, indirect effects to the terrestrial-
phase CRLF and AW via reduction in terrestrial invertebrate prey items that are exposed
to liquid and granular applications of 2,4-D are expected.
LOC exceedances:
RQs for all liquid and granular applications of 2,4-D except citrus and potato uses
exceeded the LOCs for both small and large invertebrate prey items, as well as for
earthworms.
Earthworm risks:
Risks to terrestrial invertebrates can also be estimated using the available earthworm
toxicity data. The LC50 for earthworms was 61.6 jag a.e./cm2 which is equivalent to 5.50
lb a.e./acre. RQs were calculated as a ratio of the application rate and the toxicity value
(Table 5.15). Based on these analyses, 2,4-D has the potential to indirectly affect those
listed species that rely on terrestrial invertebrates during at least some portion of their
life-cycle (i.e., CRLF and AW).
Tsihle 5.15 Acute UQs used (0 Kslimale Indirect effects lo
terrestrial-phase ( Kl.l s and AW via ingestion of
terrestrial invertebrates (represented In earthworms)
I'.r.C (II) ;i.c./;iciv) 1
Anile UQ1
0.07
0.01
0.10
0.02
0.50
0.10*
1.0
0.19*
1.36
0.25*
1.4
0.27*
1.5
0.29*
2.0
0.39*
4.0
0.78*
Single application rates from a variety of crops are represented here.
**Acute RQ > 0.05 exceeds acute level of concern (LOC) for terrestrial
invertebrates.
5.2.2.7 Frogs
Terrestrial-phase adult CRLFs and AW also consume small frogs. RQ values, estimated
using T-REX, representing direct exposures of 2,4-D to terrestrial-phase CRLFs and AW
are used to represent exposures of 2,4-D to small frogs in terrestrial habitats. The indirect
159
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effects to frogs as food items are based on the direct effects analysis for the terrestrial-
phase CRLF and AW (Section 5.2.1.2),
5.2.3 Indirect Effects (via Habitat Effects)
5.2.3.1 Aquatic Plants (Vascular and Non-vascular)
Aquatic plants serve several important functions in aquatic ecosystems. Non-vascular
aquatic plants are primary producers and provide the autochthonous energy base for
aquatic ecosystems. Vascular plants provide structure as attachment sites and refugia for
many aquatic invertebrates, fish, and juvenile organisms, such as fish and frogs. In
addition, vascular plants also provide primary productivity and oxygen to the aquatic
ecosystem. Rooted plants help reduce sediment loading and provide stability to near-
shore areas and lower streambanks. In addition, vascular aquatic plants are important as
attachment sites for egg masses of CRLFs. Potential indirect effects to the CRLF based
on impacts to habitat and/or primary production were assessed using RQs from
freshwater aquatic vascular and non-vascular plant data.
LOC exceedances:
For non-vascular plants, LOCs were exceeded for the direct application to water aquatic
weed control scenarios. For acid/salt aquatic weed control uses, the RQ was 1.03. For
ester aquatic weed control uses, the RQ was 60.61.
For vascular plants, there were several LOC exceedances for acid/salt uses for vascular
aquatic plants (see Table 5.4.a), There were no LOC exceedances for drift+runoff ester
uses and drift only ester uses that were not direct application to water. The LOC was
exceeded for the rice and all direct application to water uses for both acid/salts and esters.
Comparison of modeled to observed water concentrations:
The available monitoring data have been presented in Section 3.2.7, Compared with the
modeling results, the modeled values are much higher than USGS NAWQA and CDPR
data for California. The lack of agreement between the model and monitoring results is
not unexpected since the monitoring data were not designed to target areas of 2,4-D
usage. With the exception of direct aquatic applications, such as rice use and aquatic
weed control, the model predictions are comparable with the available registrant-
submitted fate studies.
5.2.3.2 Terrestrial Plants
Terrestrial plants serve several important habitat-related functions for the CRLF and the
AW. In addition to providing habitat and cover for invertebrate and vertebrate prey items
of the CRLF and the AW, terrestrial vegetation also provides shelter for the CRLF and
the AW and cover from predators while foraging. Terrestrial plants also provide energy
to the terrestrial ecosystem through primary production. Upland vegetation including
grassland and woodlands provides cover during dispersal. Riparian vegetation helps to
maintain the integrity of aquatic systems by providing bank and thermal stability, serving
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as a buffer to filter out sediment, nutrients, and contaminants before they reach the
watershed, and serving as an energy source.
Loss, destruction, and alteration of habitat were identified as threats to the CRLF in the
USFWS Recovery Plan (USFWS, 2002). Herbicides can adversely impact habitat in a
number of ways. In the most extreme case, herbicides in spray drift and runoff from the
site of application have the potential to kill (or reduce growth and/or biomass) all or a
substantial amount of the vegetation, thus removing or impacting structures that define
the habitat, and reducing the functions (e.g., cover, food supply for prey base) provided
by the vegetation.
Riparian vegetation typically consists of three tiers of vegetation, which include a
groundcover of grasses and forbs, an understory of shrubs and young trees, and an
overstory of mature trees. Frogs spend a considerable amount of time resting and feeding
in riparian vegetation; the moisture and cover of the riparian plant community provides
good foraging habitat and may facilitate dispersal in addition to providing pools and
backwater aquatic areas for breeding (USFWS, 2002). According to Hayes and Jennings
(1988), the CRLF tends to occupy water bodies with dense riparian vegetation including
willows (Salix sp.). Upland habitat includes grassland and woodlands, as well as
scrub/shrub habitat.
All of the modeled uses of 2,4-D exceed the Agency LOCs for risk for terrestrial plants
including both monocots and dicots. In addition, there are a multitude of reported
incidents of 2,4-D negatively impacting terrestrial plants (Section 4.4.2).
Although the terrestrial plant LOC was exceeded for Citrus and Potatoes for both CRLF
and the AW, EFED determined the effect to be insignificant as the potential small effect
on the vegetation would likely not impact the overall habitat quality. It is anticipated that
any effects would be small as the RQs only mildly exceeded the LOC.
Based on exceedances of the terrestrial plant LOCs for all 2,4-D use patterns following
runoff and spray drift to dry and semi-aquatic areas, the following general conclusions
can be made with respect to potential harm to riparian habitat:
2,4-D may enter riparian areas via runoff and/or spray drift where it may contact
foliar surfaces of emerged seedlings or form a chemical barrier on soil, which
would affect pre-emergent plants.
Based on 2,4-D's mode of action and a comparison of seedling emergence and
vegetative vigor EC25 values to EECs estimated using TerrPlant, emerging or
developing seedlings may be affected in areas receiving both runoff and drift and
in areas receiving drift alone at applications rates greater than a single application
of 0.07 lb a.e./acre. If inhibition of new growth occurs, it could result in
degradation of high quality riparian habitat over time because as older growth dies
from natural or anthropogenic causes, plant biomass may be prevented from being
replenished in the riparian area.
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In summary, terrestrial plant RQs exceed LOCs, which indicates risk to upland and
riparian vegetation. However, while it is not expected that woody plants with mature bark
are sensitive to environmentally relevant 2,4-D concentrations, the lack of a guideline
study on established woody plants precludes estimation of effects. Because upland and
riparian areas are comprised of a mixture of both woody plants and herbaceous
vegetation, terrestrial-phase CRLFs and the AW may be indirectly affected by adverse
effects solely to herbaceous vegetation, which provides habitat and cover for the CRLF,
AW and their prey.
5.2.3.2.1 Spray Drift Buffer Analysis
In order to estimate buffer distances that are protective of plant species that the terrestrial-
phase CRLF and AW or their prey may depend on for food and cover, AgDRIFT was
used to model the dissipation distance to the EC25 levels for terrestrial plants. Input
parameters for AgDRIFT for aerial and ground applications are described in Table 5.16.
For ground applications, only Tier I model estimates are available; the maximum buffer
distance that can be calculated in 1000 ft. For aerial applications, Tier I and Tier II
models provide estimates of 1000 feet or less; the Tier III model provides estimates of up
to 2640 ft.
Because 2,4-D is used as a pre-emergent and post-emergent herbicide, buffer distances
were calculated for the most sensitive endpoints for both monocots and dicots in the
seedling emergence and vegetative vigor studies. For ground application effects on
monocots, required buffer distances to eliminate LOC exceedances ranged from 0 to 115
ft. For ground application effects on dicots, required buffer distances to eliminate LOC
exceedances ranged from 16 to >1000 ft. For aerial application effects on monocots,
required buffer distances to eliminate LOC exceedances ranged from 0 to 2402 ft. For
aerial application effects on dicots, required buffer distances to eliminate LOC
exceedances ranged from 154 to >2640 ft.
This analysis did not include any mitigation resulting from the RED regarding spray drift
management requirements. If these conditions were incorporated into the analysis, it it
likely that the estimated buffer widths in Table 5.16 would be reduced.
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Tsihle 5.16 Ksliinnlion of IJulTcr Dislnncc Required lo Kliminsilc I.OC
Kxcccdsinccs (only sprsiv clril'l exposure considered) lor Tcrrcslrisil 1*1:1 ills IJsiscd
on A«I)UII 1
l(:;
(II) a.c./ac)
l-'raclion of applied
= I'.Cv;- Rale
BulTcr \\ id 111.
aei'ial (ID 1
ISulTcr \\ idlli.
liround (ID:
Appliciili«ui Kiilo = 0.0'7 Ih a.c./ac
Seedlins Emersence
Monocots
0.097
1.386
0
(TI)
0
Seedlins Emersence
Dicots
0.012
0.171
154.2
(TI)
16.4
Vesetative Visor
Monocots
0.088
1.257
0
(TI)
0
Vesetative Visor
Dicots
0.0021
0.03
1807.72
(Till)
85.3
A
)|)lication Rate = 0.1 lb a.c./ac
Seedlins Emersence
Monocots
0.097
0.97
0
(TI)
3.28
Seedlins Emersence
Dicots
0.012
0.12
242.78
(TI)
22.97
Vesetative Visor
Monocots
0.088
0.88
0
(TI)
3.28
Vesetative Visor
Dicots
0.0021
0.021
2480.29
(Till)
118.11
A
>plicalion Rale = 0.5 lb a.c./ac
Seedlins Emersence
Monocots
0.097
0.194
131.23
(TI)
16.4
Seedlins Emersence
Dicots
0.012
0.024
2250.63
(Till)
104.99
Vesetative Visor
Monocots
0.088
0.176
150.92
(TI)
16.4
Vesetative Visor
Dicots
0.0021
0.0042
>2640
(Till)
475.72
Application Rale = 1 II)
Seedlins Emersence
Monocots
0.097
0.097
318.24
(TI)
29.53
Seedlins Emersence
Dicots
0.012
0.012
>2640
(Till)
200.13
Vesetative Visor
Monocots
0.088
0.088
357.61
(TI)
29.53
Vesetative Visor
Dicots
0.0021
0.0021
>2640
(Till)
770.99
Application Rate = 1.36 lb a.c./ac
Seedlins Emersence
Monocots
0.097
0.0713
465.87
(TI)
36.09
Seedlins Emersence
Dicots
0.012
0.0088
>2640
(Till)
265.74
Vesetative Visor
Monocots
0.088
0.0647
524.93
(TI)
39.37
Vesetative Visor
Dicots
0.0021
0.00154
>2640
(Till)
944.87
Applicalion Ra(c = 1.4 II) a.c./ac
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Table 5.16 Kslimation of ISnITer Distance Required to l.liniinale I.OC
Kxcecdances (only spray drift exposure considered) lor Terrestrial Plants Based
on A«I)UII 1
I(:;
(II) il.C./ilC)
l-'raelion ol'applied
= l.( Rale
liulTer \\ id 111.
aerial (ID 1
ISii ITer \\ id 111.
liround (I'l)"
Seedlins Emersence
Monocots
0.097
0.0693
482.28
(TI)
39.37
Seedlins Emersence
Dicots
0.012
0.00857
>2640 (Till)
269.03
Vesetative Visor
Monocots
0.088
0.062857
547.89
(TI)
42.65
Vesetative Visor
Dicots
0.0021
0.0015
>2640 (Till)
961.27
A
)pliealiun Ra(e = 1.5 II) a.e./ae
Seedlins 1 !meiseiice
Monocots
0 <)')"
() u<4<>"
52X : 1
(TI)
,<)
Seedlins Emersence
Dicots
0.012
0.008
>2640 (Till)
285.43
Vesetative Visor
Monocots
0.088
0.05867
600.39
(TI)
45.93
Vesetative Visor
Dicots
0.0021
0.0014
>2640 (Till)
>1000
A
iplication Rate = 2.0 lb a.c./ac
Seedlins Emersence
Monocots
0.097
0.0485
777.55
(TI)
52.49
Seedlins Emersence
Dicots
0.012
0.006
>2640 (Till)
360.89
Vesetative Visor
Monocots
0.088
0.044
905.5
(TI)
59.05
Vesetative Visor
Dicots
0.0021
0.00105
>2640 (Till)
>1000
A
iplication Rate = 4.0 lb a.c./ac
Seedlins Emersence
Monocots
0.097
0.02425
2230.94
(Till)
104.99
Seedlins Emersence
Dicots
0.012
0.003
>2640 (Till)
606.95
Vesetative Visor
Monocots
0.088
0.022
2401.55
(Till)
114.83
Vesetative Visor
Dicots
0.0021
0.000525
>2640 (Till)
>1000
Serial application scenarios are modeled with AgDrift Tier I (TI) and AgDrift Tier III (Till).
2Ground application scenarios are modeled with AgDrift Tier I, no higher tiers available.
5.2.4 Modification to Designated Critical Habitat
5.2.4.1 Aquatic-phase PCEs
Three of the four assessment endpoints for the aquatic-phase primary constituent
elements (PCEs) of designated critical habitat for the CRLF are related to potential
effects to aquatic and/or terrestrial plants:
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Alteration of channel/pond morphology or geometry and/or increase in sediment
deposition within the stream channel or pond: aquatic habitat (including riparian
vegetation) provides for shelter, foraging, predator avoidance, and aquatic
dispersal for juvenile and adult CRLFs.
Alteration in water chemistry/quality including temperature, turbidity, and oxygen
content necessary for normal growth and viability of juvenile and adult CRLFs
and their food source.
Reduction and/or modification of aquatic-based food sources for pre-metamorphs
(e.g., algae).
Conclusions for potential indirect effects to the CRLF via direct effects to aquatic and
terrestrial plants are used to determine whether modification to critical habitat may occur.
There is a potential for habitat modification via impacts to aquatic plants (Sections
5.2.2.1 and 5.2.3.1) and terrestrial plants (Section 5.2.3.2)
The remaining aquatic-phase PCE is "alteration of other chemical characteristics
necessary for normal growth and viability of CRLFs and their food source." Other than
impacts to algae as food items for tadpoles (discussed above), this PCE is assessed by
considering direct and indirect effects to the aquatic-phase CRLF via acute and chronic
freshwater fish and invertebrate toxicity endpoints as measures of effects. There is a
potential for habitat modification via impacts to aquatic-phase CRLFs (Section 5.2.1.1)
and effects to freshwater invertebrates and fish as food items (Sections 5.2.2.2 and
5.2.2.3),
5.2.4.2 Terrestrial-Phase PCEs
Two of the four assessment endpoints for the terrestrial-phase PCEs of designated critical
habitat for the CRLF and AW are related to potential effects to terrestrial plants:
Elimination and/or disturbance of upland habitat; ability of habitat to support food
source of CRLFs and AWs: Upland areas within 200 ft of the edge of the riparian
vegetation or drip line surrounding aquatic and riparian habitat that are comprised
of grasslands, woodlands, and/or wetland/riparian plant species that provide the
CRLF and AW shelter, forage, and predator avoidance.
Elimination and/or disturbance of dispersal habitat: Upland or riparian dispersal
habitat within designated units and between occupied locations within 0.7 mi of
each other that allow for movement between sites including both natural and
altered sites which do not contain barriers to dispersal.
As discussed above, there is potential for habitat modification of the terrestrial-phase
CRLF and AW via impacts to terrestrial plants as indicated by potential impacts to
herbaceous vegetation, which provides habitat, cover, and a means of dispersal for the
terrestrial-phase CRLF and AW and their prey. This habitat modification could be caused
by all modeled uses of 2,4-D at the maximum labeled rate.
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The third terrestrial-phase PCE is "reduction and/or modification of food sources for
terrestrial phase juveniles and adults." To assess the impact of 2,4-D on this PCE, acute
toxicity endpoints for terrestrial invertebrates and acute and chronic toxicity endpoints for
mammals and terrestrial-phase frogs are used as measures of effects. Based on the
characterization of indirect effects to the terrestrial-phase CRLF and the AW via
reduction in prey base (Section 5.2.2.4 for terrestrial invertebrates, Section 5.2.2.5 for
mammals, and Section 5.2.2.6 for frogs), there is potential for critical habitat
modification via a reduction of terrestrial invertebrates, small mammals, and frogs as
food items.
The fourth terrestrial-phase PCE is based on alteration of chemical characteristics
necessary for normal growth and viability of juvenile and adult CRLFs, as well as the
AW, and their food sources. As discussed in Section 5.2.1.2, direct acute effects to the
terrestrial-phase CRLF and the AW are likely. Indirect effects to the terrestrial-phase
CRLF and AW via reduction in prey base are likely. Therefore, there is potential for
habitat modification via direct and indirect effects to the terrestrial-phase CRLF and AW.
6. Uncertainties
6.1 Exposure Assessment Uncertainties
6.1.1 Maximum Use Scenario
The screening-level risk assessment focuses on characterizing potential ecological risks
resulting from a maximum use scenario, which is determined from labeled statements of
maximum application rate and number of applications with the shortest time interval
between applications. The frequency at which actual uses approach this maximum use
scenario may be dependent on pest resistance, timing of applications, cultural practices,
and market forces.
6.1.2 Usage Uncertainties
County-level usage data were obtained from California's Department of Pesticide
Regulation Pesticide Use Reporting (CDPR PUR) database. Eight years of data (1999 -
2006) were included in this analysis. CDPR PUR documentation indicates that errors in
the data may include the following: a misplaced decimal; incorrect measures, area
treated, or units; and reports of diluted pesticide concentrations. In addition, it is possible
that the data may contain reports for pesticide uses that have been cancelled. The CDPR
PUR data does not include homeowner-applied pesticides; therefore, residential uses are
not likely to be reported. As with all pesticide usage data, there may be instances of
misuse and misreporting. The Agency made use of the most current, verifiable
information; in cases where there were discrepancies, the most conservative information
was used.
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6.1.3 Aquatic Exposure Modeling of 2,4-D
Aquatic exposures are quantitatively estimated for all of the assessed uses using scenarios
that represent high exposure sites for 2,4-D application. The standard ecological water
body scenario (EXAMS pond) used to calculate potential aquatic exposure to pesticides
is intended to represent conservative estimates and to avoid underestimations of the
actual exposure. Each of these sites represents a 10-hectare field that drains into a 1-
hectare pond, which is 2 meters deep and has no outlet. Exposure estimates generated
using the standard pond are intended to represent a wide variety of vulnerable water
bodies that occur at the top of watersheds including prairie pot holes, playa lakes,
wetlands, vernal pools, man-made and natural ponds, and intermittent and first-order
streams. As a group, there are factors that make these water bodies more or less
vulnerable than the standard surrogate pond. Static water bodies that have larger ratios of
drainage area to water body volume would be expected to have higher peak EECs than
the standard pond. These water bodies will be either shallower or have large drainage
areas (or both). Shallow water bodies tend to have limited additional storage capacity
and, thus, tend to overflow and carry pesticide in the discharge whereas the standard pond
has no discharge. As watershed size increases beyond 10 hectares, at some point, it
becomes unlikely that the entire watershed is planted to a single crop, which is all treated
with the pesticide. Headwater streams can also have peak concentrations higher than the
standard pond, but they tend to persist for only short periods of time and are then carried
downstream.
6.1.3.1 PRZM/EXAMS
The Agency acknowledges that there are some unique aquatic habitats that are not
accurately captured by this modeling scenario and modeling results may, therefore,
under- or over-estimate exposure, depending on a number of variables. For example,
some organisms may inhabit water bodies of different size and depth and/or are located
adjacent to larger or smaller drainage areas than the EXAMS pond. In addition, the
Services agree that the existing EXAMS pond represents the best currently available
approach for estimating aquatic exposure to pesticides (USFWS/NMFS, 2004).
In general, the linked PRZM/EXAMS model produces estimated aquatic concentrations
that are expected to be exceeded once within a ten-year period. The Pesticide Root Zone
Model is a process or "simulation" model that calculates what happens to a pesticide in
an agricultural field on a day-to-day basis. It considers factors such as rainfall and plant
transpiration of water, as well as how and when the pesticide is applied. It has two major
components: hydrology and chemical transport. Water movement is simulated by the use
of generalized soil parameters, which include field capacity, wilting point, and saturation
water content. The chemical transport component can simulate pesticide application on
the soil or on the plant foliage. Dissolved, adsorbed, and vapor-phase concentrations in
the soil are estimated by simultaneously considering the processes of pesticide uptake by
plants, surface runoff, erosion, decay, volatilization, foliar wash-off, advection,
dispersion, and retardation.
167
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Uncertainties associated with each of these individual components add to the overall
uncertainty of the modeled concentrations. Additionally, model inputs from the
environmental fate degradation studies are chosen to represent the upper confidence
bound on the mean values that are not expected to be exceeded in the environment
approximately 90 percent of the time. Mobility input values are chosen to be
representative of conditions in the environment. The natural variation in soils adds to the
uncertainty of modeled values. Factors such as application date, crop emergence date,
and canopy cover can also affect estimated concentrations, adding to the uncertainty of
modeled values. Factors within the ambient environment such as soil temperatures,
sunlight intensity, antecedent soil moisture, and surface water temperatures can cause
actual aquatic concentrations to differ for the modeled values.
Unlike spray drift, tools are currently not available to evaluate the effectiveness of a
vegetative setback on runoff and loadings. The effectiveness of vegetative setbacks is
highly dependent on the condition of the vegetative strip. For example, a well-
established, healthy vegetative setback can be a very effective means of reducing runoff
and erosion from agricultural fields. Alternatively, a setback of poor vegetative quality
or a setback that is channelized can be ineffective at reducing loadings. Until a
quantitative method to estimate the effect of vegetative setbacks on various conditions on
pesticide loadings becomes available, the aquatic exposure predictions are likely to
overestimate exposure where healthy vegetative setbacks exist and underestimate
exposure where poorly developed, channelized, or bare setbacks exist.
In order to account for uncertainties associated with modeling, available monitoring data
were compared to PRZM/EXAMS estimates of peak EECs for the different uses. As
previously discussed, several data values were available from NAWQA for 2,4-D
concentrations measured in surface waters receiving runoff from agricultural areas. The
specific use patterns (e.g., application rates and timing, crops) associated with the
agricultural areas are unknown; however, they are assumed to be representative of
potential 2,4-D use areas. The available monitoring data were presented in Section 3.2.4,
Compared with the modeling results, the NAWQA and CDPR monitoring data values are
lower than PRZM/EXAMS modeling results. These findings may be because the
monitoring data were not designed specifically for 2,4-D use areas. Most model
predictions obtained by PRZM/EXAMS are comparable with the available registrant-
submitted field dissipation studies.
6.1.3.2 Direct Application to Water
Because there are no existing modeling scenarios for direct application to water, a first
approximation of an EEC was predicted assuming direct application to the standard pond.
For this assessment, EFED utilized a first-order decay model to estimate average
concentrations that incorporates degradation based on an acceptable aerobic aquatic
metabolism study (ti/2 =15 days, used input value of 45 days per EFED Guidance) for the
EFED standard pond with no flow. This approach does not account for other types of
degradation that may occur or for 2,4-D that is no longer available to aquatic plants and
organisms due to sorption to sediment.
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6.1.3.3 Rice Application Model
Estimates from the Tier I model generally do not represent typical concentrations found
in human drinking water, as they represent paddy discharge water. However, these
concentrations may be a reasonable estimate of acute concentrations for use in an
ecological assessment where exposure occurs at or near the rice paddy. For both human
drinking water and ecological exposure, the chronic concentrations, as well as offsite
concentrations, are expected to be conservative. A higher tier rice model should be used
to estimate chronic exposure to compounds that degrade rapidly into degradates that are
not of risk concern.
If Tier I estimates calculated by this screening method do not exceed the level of concern
in a risk assessment, there is high confidence that there will be little or no risk above the
level of concern from exposure through water resources. However, when a level of
concern is exceeded, it cannot be determined whether the exceedance will in fact occur or
whether this method has overestimated the exposure because of the uncertainties
associated with the screening method.
6.1.4 Potential Groundwater Contributions to Surface Water Chemical
Concentrations
Although the potential impact of discharging groundwater on CRLF populations is not
explicitly delineated, it should be noted that groundwater could provide a source of
pesticide to surface water bodies - especially low-order streams, headwaters, and
groundwater-fed pools. This is particularly likely if the chemical is persistent and
mobile. Soluble chemicals that are primarily subject to photolytic degradation will be
very likely to persist in groundwater and can be transported over long distances.
Similarly, many chemicals degrade slowly under anaerobic conditions (common in
aquifers) and are thus more persistent in groundwater. Much of this groundwater will
eventually be discharged to the surface - often supporting stream flow in the absence of
rainfall. Continuously flowing low-order streams, in particular, are sustained by
groundwater discharge, which can constitute 100% of stream flow during baseflow (no
runoff) conditions. Thus, it is important to keep in mind that pesticides in groundwater
may have a major detrimental impact on surface water quality and on CRLF habitats.
SCI-GROW may be used to determine likely 'high-end' groundwater vulnerability, with
the assumption (based upon persistence in hypoxic or anoxic conditions, and mobility)
that much of the compound entering the groundwater will be transported some distance
and eventually discharged into surface water. Although concentrations in a receiving
water body resulting from groundwater discharge cannot be explicitly quantified, it
should be assumed that significant attenuation and retardation of the chemical will have
occurred prior to discharge. Nevertheless, groundwater could still be a significant,
consistent source of chronic background concentrations in surface water and may also
add to surface runoff during storm events (as a result of enhanced groundwater discharge
typically characterized by the 'tailing limb' of a storm hydrograph).
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6.1.5 Terrestrial Exposure Modeling of 2,4-D
The Agency relies on the work of Fletcher et al. (1994) for setting the assumed pesticide
residues in wildlife dietary items. These residue assumptions are believed to reflect a
realistic upper-bound residue estimate, although the degree to which this assumption
reflects a specific percentile estimate is difficult to quantify. It is important to note that
the field measurement efforts used to develop the Fletcher estimates of exposure involve
highly varied sampling techniques. It is entirely possible that much of these data reflect
residues averaged over entire above-ground plants in the case of grass and forage
sampling.
It was assumed that ingestion of food items in the field occurs at rates commensurate
with those in the laboratory. Although the screening assessment process adjusts dry-
weight estimates of food intake to reflect the increased mass in fresh-weight wildlife food
intake estimates, it does not allow for gross energy differences. Direct comparison of a
laboratory dietary concentration-based effects threshold to a fresh-weight pesticide
residue estimate would result in an underestimation of field exposure by food
consumption by a factor of 1.25 - 2.5 for most food items.
Differences in assimilative efficiency between laboratory and wild diets suggest that
current screening assessment methods do not account for a potentially important aspect of
food requirements. Depending upon species and dietary matrix, bird assimilation of wild
diet energy ranges from 23 - 80%, and mammal's assimilation ranges from 41 - 85%
(U.S. EPA, 1993). If it is assumed that laboratory chow is formulated to maximize
assimilative efficiency (e.g., a value of 85%), a potential for underestimation of exposure
may exist by assuming that consumption of food in the wild is comparable with
consumption during laboratory testing. In the screening process, exposure may be
underestimated because metabolic rates are not related to food consumption.
For the terrestrial exposure analysis of this risk assessment, a generic bird or mammal
was assumed to occupy either the treated field or adjacent areas receiving a treatment rate
on the field. Actual habitat requirements of any particular terrestrial species were not
considered, and it was assumed that species occupy, exclusively and permanently, the
modeled treatment area. Spray drift model predictions suggest that this assumption leads
to an overestimation of exposure to species that do not occupy the treated field
exclusively and permanently.
6.1.6 Spray Drift Modeling
Although there may be multiple 2,4-D applications at a single site, it is unlikely that the
same organism would be exposed to the maximum amount of spray drift from every
application made. In order for an organism to receive the maximum concentration of 2,4-
D from multiple applications, each application of 2,4-D would have to occur under
identical atmospheric conditions (e.g., same wind speed and - for plants - same wind
direction), and (if it is an animal) the animal being exposed would have to be present
170
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directly downwind at the same distance after each application. Although there may be
sites where the dominant wind direction is fairly consistent (at least during the relatively
quiescent conditions that are most favorable for aerial spray applications), it is,
nevertheless, highly unlikely that plants in any specific area would receive the maximum
amount of spray drift repeatedly. It appears that in most areas, based upon available
meteorological data, wind direction is temporally variable, even within the same day.
Additionally, other factors including variations in topography, cover, and meteorological
conditions over the transport distance are not accounted for by the AgDRIFT model (i.e.,
spray drift from aerial and ground applications in a flat area with little to no ground cover
and a steady, constant wind speed and direction is modeled). Therefore, in most cases,
the drift estimates from AgDRIFT may overestimate exposure even from single
applications, especially as the distance increases from the site of application, since the
model does not account for potential obstructions (e.g., large hills, berms, buildings,
trees, etc.). Furthermore, conservative assumptions are often made regarding the droplet
size distributions being modeled (e.g., 'ASAE Very Fine to Fine' for orchard uses and
' ASAE Very Fine' for agricultural uses), the application method (e.g., aerial), release
heights and wind speeds. Alterations in any of these inputs would change the area of
potential effect.
The analysis conducted in this assessment did not include any mitigation resulting from
the RED regarding spray drift management requirements. If these conditions were
incorporated into the analysis, it it likely that the estimated buffer widths would be
reduced.
6.2 Effects Assessment Uncertainties
6.2.1 Age Class and Sensitivity of Effects Thresholds
It is generally recognized that test organism age may have a significant impact on the
observed sensitivity to a toxicant. The acute toxicity data for fish are collected on
juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on
recommended immature age classes (e.g., first instar for daphnids; second instar for
amphipods, stoneflies, and mayflies; and third instar for midges).
Testing of juveniles may overestimate toxicity at older age classes for pesticide active
ingredients that act directly without metabolic transformation because younger age
classes may not have the enzymatic systems associated with detoxifying xenobiotics. In
so far as the available toxicity data providing ranges of sensitivity information with
respect to age class, this assessment uses the most sensitive life-stage information as
measures of effect for surrogate animals and is, therefore, considered as protective of the
assessed species.
Additionally, variation in toxicity was observed when temperature or pH was adjusted in
a few aquatic studies. For example, one study (E006387) observed an increase in toxicity
to Cyprinus carpio with corresponding increases in temperature. Another study (E61180)
observed increased toxicity with lower pH's; when pH was adjusted to remain between
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7.0 and 7.4, the LC50 value increased approximately 10-fold. While the studies that
produced toxicity values that were used quantitatively generally adhered to guideline test
conditions, uncertainties remain of the effects of 2,4-D in the environment given the
likelihood for variable temperature, pH, and other conditions.
6.2.2 Use of Surrogate Species Effects Data
Freshwater fish are used as surrogate species for aquatic-phase amphibians. Although,
acute amphibian data are available for 2,4-D (ester and acid), the available open literature
information on 2,4-D toxicity to aquatic-phase amphibians shows that acute ecotoxicity
endpoints for aquatic-phase amphibians are generally about 7 times less sensitive than
freshwater fish for exposure to acid /salts (common carp LC50 = 24.15 mg a.e./L; Western
chorus frog tadpoles LC50 = 181 mg a.e./L) and 2 times less sensitive than freshwater fish
for exposure to esters (bluegill sunfish LC50 = 0.26 mg a.e./L; leopard frog tadpoles LC50
= 0.505 mg a.e./L ). Therefore, endpoints based on freshwater fish ecotoxicity data are
assumed to be protective of potential direct effects to aquatic-phase amphibians including
the CRLF, and extrapolation of the risk conclusions from the most sensitive tested
species to the aquatic-phase CRLF is likely to overestimate the potential risks to those
species. Efforts are made to select the organisms most likely to be affected by the type of
compound and usage pattern; however, there is an inherent uncertainty in extrapolating
across phyla. In addition, the Agency's LOCs are intentionally set very low, and
conservative estimates are made in the screening level risk assessment to account for
these uncertainties.
As previously discussed in the aquatic toxicity portion of this assessment (Section 4.2),
aquatic amphibian data were submitted by the registrant and available in the open
literature. However, since these data were less sensitive than the freshwater fish data and
it is unknown where the CRLF falls on a sensitivity distribution for amphibians or for
aquatic vertebrate species, EFED selected the most sensitive aquatic vertebrate toxicity
test for risk estimation. For further characterization, EFED also calculated acute RQs
using the most sensitive amphibian data for acid/salts and for esters (discussed in Section
5.2.1.1)
Acceptable guideline toxicity tests and open literature studies for reptiles are not
currently available for quantitative use to assess potential risks of 2,4-D use in California
to the AW. Therefore, toxicity data for surrogate species (i.e., birds for reptiles) are used
in some instances to assess risks. Efforts are made to select the organisms, which are
most likely to be affected by the type of compound and usage pattern; however, there is
an inherent uncertainty in extrapolating across phyla. In addition, the Agency's LOCs
are intentionally set very low, and conservative estimates are made in the screening level
risk assessment to account for these uncertainties.
6.2.3 Sublethal Effects
When assessing acute risk, the screening-level risk assessment relies on the acute
mortality endpoint as well as a suite of sublethal responses to the pesticide, as determined
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by the testing of species response to chronic exposure conditions and subsequent chronic
risk assessment. Consideration of additional sublethal data in the effects determination is
exercised on a case-by-case basis and only after careful consideration of the nature of the
sublethal effect measured and the extent and quality of available data to support
establishing a plausible relationship between the measure of effect (sublethal endpoint)
and the assessment endpoints. However, the full suite of sublethal effects from valid
open literature studies is considered for the purposes of defining the action area.
Although the full suite of sublethal endpoints potentially available in the effects literature
(regardless of their significance to the assessment endpoints) are often considered to
define the action area for other chemicals, in the case of 2,4-D, LOC exceedances are
expected to occur on all land cover types throughout the state of California as a result of
this federal action and the final full extent of the action area is assumed to encompass the
entire state. To the extent to which sublethal effects are not considered in this assessment,
the potential direct and indirect effects of 2,4-D on listed species may be underestimated.
A detailed spreadsheet of the available ECOTOX open literature data, which includes the
full suite of sublethal endpoints, is presented in Appendix G.
7. Risk Conclusions
In fulfilling its obligations under Section 7(a)(2) of the Endangered Species Act, the
information presented in this endangered species risk assessment represents the best data
currently available to assess the potential risks of 2,4-D to the CRLF and AW and their
designated critical habitats.
Based on the best available information, the Agency makes a "may affect and likely to
adversely affect" (LAA) determination for both the CRLF and the AW for all assessed
use of 2,4-D except Citrus and Potatoes; the LAA is based on both direct and indirect
effects to the CRLF and AW. For Citrus and Potatoes, the Agency makes a "may affect
but not likely to adversely affect" (NLAA) determination for both the CRLF and AW
from the assessed uses of 2,4-D:
Although the mammalian dose-based chronic LOC was exceeded for both the
CRLF and the AW prey, EFED determined that this effect would be insignificant
as the potential small effect on mammal reproduction (as prey of the CRLF and
AW) would not likely impact the overall prey base. It is anticipated that any
effects would be small since the RQs only mildly exceeded the LOC.
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Although the avian acute dose-based LOC was exceeded for AW prey, EFED
determined that this effect was discountable and insignificant as the predicted
percentage of acute effect was only 0.0033% of the bird population (birds as prey
items of the AW), and if even if this effect did occur, the overall prey base of the
AW would likely not be affected.
Although the terrestrial plant LOC was exceeded for both CRLF and the AW,
EFED determined the effect to be insignificant as the potential small effect on the
vegetation would likely not impact the overall habitat quality. It is anticipated that
any effects would be small as the RQs only mildly exceeded the LOC.
Based on potential for effects across several taxa, all currently registered uses of 2,4-D in
California except Citrus and Potatoes have the potential to cause indirect effects to the
CRLF and the AW. Additionally, the Agency has determined that there is potential for
modification of the designated critical habitat of the CRLF for all assessed uses of 2,4-D
except Citrus and Potatoes based on effects to terrestrial and aquatic plants. For the AW,
based on effects to terrestrial plants, all relevant (risks of aquatic weed control uses to
terrestrial plants were not estimated) assessed uses of 2,4-D except Citrus and Potatoes
have the potential to modify the designated critical habitat. Both species may experience
modification of their designated critical habitats through reduction of prey items. Given
the LAA determinations for the CRLF and the AW for all but two assessed uses and
potential modification of designated critical habitat for all but two uses, a description of
the baseline status and cumulative effects for the CRLF is provided in Attachment 2 and
the baseline status and cumulative effects for the AW is provided in Attachment 4.
A summary of the risk conclusions and effects determinations for the CRLF and AW and
their critical habitats, given the uncertainties discussed in Section 6, is presented in
Tables 7.1 and 7.2.
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Table 7.1 KITeels Detenuin;ilion Siiinniiirv lor (lie KITccls of 2.4-1) on (lie CUM'' and AW
r.nripnim
i.nw-is
Doloi'iniiiiilion 1
ISiisis lor Doloriniiiiilioii
Sui'\ i\ al, glow ill,
Polcnlhil lor Dircii I'.ITocls
and/or reproduction
ofCRLF
individuals
LAA2
Aquatic-phase (l-Xr!s> l.arvae, ami At/alls) l icsliw alcr lisli dala used as
surrogate for CRLF.
Adult survival: Acute LOC was exceeded in the aerial forestry, tree and brush
control drift+runoff ester uses and all direct application to water scenarios.
The chance of individual effects (i.e., mortality) for freshwater fish (surrogate for
aquatic-phase CRLFs) is as high as ~1 in 1 for direct water applications.
Out of 26 incidents reported for aquatic organisms for 2,4-D acid and DMA salt,
7 registered uses were reported with certainties of highly probable(2),
probable(2) and possible (2). Incidents for 2,4-D were filed on aquatic organisms
from runoff or drift. Use sites for the above incidents were reported on
home/lawn, corn, agricultural areas, rights of way/railroad, lake, pond, stream,
turf/golf course.
Growth and reproduction: Chronic LOC was not exceeded for any scenarios.
Terrestrial-phase (Juveniles and Adults) : Avian data used as surrogate for
CRLF.
Survival: Acute LOC was exceeded in all modeled scenarios except citrus and
potatoes for liquid applications. Acute LOC was exceeded in field corn, popcorn,
sweet corn, grain or forage sorghum, non-cropland, ornamental turf, grass grown
for sod, and all direct water application scenarios (ditchbanks) for granular
applications.
The chance of individual effects (i.e., mortality) for terrestrial-phase CRLF
(Avian data used as surrogate for CRLF) is as high as ~1 in 1 for direct water
applications (ditchbanks), non-cropland, forestry, tree and brush control, and
grass grown for sod applications.
Based on one incident report from runoff, 2,4-D has been implicated as being
toxic to birds with probable certainty for a use of undetermined legality.
Growth and reproduction: Dietary-based chronic RQ values exceeded the LOC
at 1 app @ 54 lb a.e./acre for aquatic weed control (ditchbanks) for liquid
applications derived from T-REX and T-HERPS modeled scenarios.
Pulcnlhil lor Indirect l.l'IWis
Aquatic prey items, aquatic habitat, cover and/or primary productivity
Non-vascular aquatic plants: LOC was exceeded for all direct surface aquatic
weed control scenarios.
Vascular aquatic plants: LOC was exceeded for several acid/salt use scenarios
and all direct application to water scenarios.
Freshwater invertebrates: Acute LOC was exceeded for all direct application to
water scenarios. Based on the results of probit analysis, there is a significant
chance (> 10%) that direct applications to water (aquatic weed control ester
uses) will impact prey of the CRLF via direct effects on aquatic invertebrates as
dietary food items.
Freshwater fish: Acute LOC was exceeded for aerial forestry, tree and brush
control, and all direct application to water scenarios. Based on the results of
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probit analysis, there is a significant chance (> 10%) that direct applications to
water will impact prey of the CRLF via direct effects on freshwater fish as
dietary food items.
Out of 26 incidents reported for aquatic organisms for 2,4-D acid and DMA
salt, 6 registered uses were reported with certainties of highly probable(2),
probable(2) and possible (2). Incidences for 2,4-D were filed on aquatic
organisms from runoff or drift. Use sites for the above incidents were reported
on home/lawn, corn, agricultural areas, rights of way/railroad, lake, pond,
stream, turf/golf course.
Terrestrial prey items, riparian habitat
Terrestrial invertebrates: Acute LOC for small insects was exceeded for all
scenarios except citrus and potatoes. Acute LOC for large insects was exceeded
for several scenarios.
Terrestrial-phase amphibians, acute toxicity. Acute LOCs were exceeded in all
T-REX and T-HERPS modeled scenarios except citrus and potatoes for liquid
applications. Acute LOC was exceeded in field corn, popcorn, sweet corn, grain
or forage sorghum, non-cropland, ornamental turf, grass grown for sod and all
direct water application scenarios (ditchbanks) for T-REX modeled granular
applications.
The chance of individual effects (i.e., mortality) for terrestrial-phase CRLF
(Avian data used as surrogate for CRLF) is as high as ~1 in 1 for direct water
applications (ditchbanks), non-cropland, forestry, tree and brush control, and
grass grown for sod applications.
Terrestrial-phase amphibians, growth and reproduction: Dietary-based chronic
RQ values exceeded the LOC at 1 app @ 54 lb a.e./acre for aquatic weed
control (ditchbank exposure) for liquid application.
Small terrestrial mammals, acute toxicity: Acute LOC was exceeded in all
modeled scenarios except citrus and potatoes for liquid applications. Acute LOC
was exceeded in field corn, popcorn, sweet corn, grain or forage sorghum, non-
cropland, ornamental turf, grass grown for sod and all direct water application
scenarios (ditchbanks) for granular applications.
Based on the results of probit analysis, there is a significant chance (> 10%) that
several of the 2,4-D uses will impact prey of the CRLF via direct effects on
mammals as dietary food items.
Based on three incident reports, 2,4-D has been implicated as being toxic to
mammals with possible and probable certainty for registered and undetermined
use legalities.
Small terrestrial mammals, growth and reproduction: For liquid applications of
2,4-D, chronic dose-based LOCs were exceeded for all application scenarios.
Chronic-dietary based RQ values exceeded the LOC for all liquid application
scenarios except potatoes and citrus.
Terrestrial plants: LOCs were exceeded for monocots for all modeled scenarios
except citrus and potatoes. LOCs were exceeded for dicots for all modeled
scenarios.
For 2,4-D, 358 incidents were reported for mostly plant damage to a wide variety
of terrestrial plants particularly from direct treatment or spray drift. 140 of these
incidents were registered uses and 143 were of unknown legality. The majority
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of the reports were of possible to highly probable certainty. Other reported
incident exposures included spills, stunted growth, discoloration, runoff,
persistence in crop and carryover.
Survival, growth,
and/or reproduction
of AW individuals
Pulcnlhil lor Direct I-'. 11 eels
Terrestrial-phase (Juveniles and Adults): Avian data used as surrogate for AW.
Survival: Acute LOC was exceeded in all modeled scenarios except citrus and
potatoes for liquid applications. Acute LOC was exceeded in field corn, popcorn,
sweet corn, grain or forage sorghum, non-cropland, ornamental turf, grass grown
for sod, and all direct water application scenarios (ditchbanks) for granular
applications.
The chance of individual effects (i.e., mortality) for AW (Avian data used as
surrogate for AW) is as high as ~1 in 1 for direct water application (ditchbanks).
Based on one incident report 2,4-D, has been implicated as being toxic to birds
with probable certainty for an undetermined use legality.
Growth and reproduction: Dietary-based chronic RQ values exceeded the LOC
at 1 app @ 54 lb a.e./acre for aquatic weed control (ditchbanks) for liquid
application.
I'olonliiil lor Indireel I". Heels
Terrestrial prey items, riparian habitat
Terrestrial invertebrates: Acute LOC for small insects was exceeded for all
scenarios except citrus and potatoes. Acute LOC for large insects was exceeded
for several scenarios.
Terrestrial-phase amphibians, acute toxicity: Acute LOCs were exceeded in all
T-REX and T-HERPS modeled scenarios except citrus and potatoes for liquid
applications. Acute LOC was exceeded in field corn, popcorn, sweet corn, grain
or forage sorghum, non-cropland, ornamental turf, grass grown for sod, and all
direct water application scenarios (ditchbanks) for T-REX modeled granular
applications.
The chance of individual effects (i.e., mortality) for terrestrial-phase CRLF
(Avian data used as surrogate for CRLF) is as high as ~1 in 1 for direct water
application (ditchbanks).
Terrestrial-phase amphibians, growth and reproduction: Dietary-based chronic
RQ values exceeded the LOC at 1 app @ 54 lb a.e./acre for aquatic weed
control (ditchbank exposure) for liquid application.
Small terrestrial mammals, acute toxicity: Acute LOC was exceeded in all
modeled scenarios except citrus and potatoes for liquid applications. Acute LOC
was exceeded in field corn, popcorn, sweet corn, grain or forage sorghum, non-
cropland, ornamental turf, grass grown for sod, and all direct water application
scenarios (ditchbanks) for granular applications.
Based on the results of probit analysis, there is a significant chance (> 10%) that
several of the 2,4-D uses will impact prey of the AW via direct effects on
mammals as dietary food items.
Based on three incident reports, 2,4-D has been implicated as being toxic to
animals with possible and probable certainty for registered and undetermined use
legalities.
Small terrestrial mammal, growth and reproduction'. For liquid applications of
2,4-D, chronic dose-based LOCs were exceeded for all application scenarios.
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Chronic-dietary-based RQ values exceeded the LOC for all liquid application
scenarios except potatoes and citrus.
Birds, acute toxicity: Acute LOC was exceeded in all modeled scenarios for
liquid applications. Acute LOC was exceeded in field corn, popcorn, sweet corn,
grain or forage sorghum, non-cropland, ornamental turf, grass grown for sod, and
all direct water application scenarios (ditchbank exposure) for granular
applications.
Based on the results of probit analysis, there is a significant chance (> 10%) that
all uses except potatoes and citrus uses will impact prey of the AW via direct
effects on birds as dietary food items.
Based on one incident report, 2,4-D has been implicated as being toxic to
animals with probable certainty for an undetermined use legality.
Birds, growth and reproduction: Dietary-based chronic RQ values exceeded the
LOC at 1 app @ 54 lb a.e./acre for aquatic weed control (ditchbank exposure) for
liquid application.
Terrestrial plants: LOCs were exceeded for monocots for all modeled scenarios
except citrus and potatoes. LOCs were exceeded for dicots for all modeled
scenarios.
For 2,4-D, 358 incidents were reported for mostly plant damage to a wide variety
of terrestrial plants particularly from direct treatment or spray drift. 140 of these
incidents were registered uses and 143 were of unknown legality. The majority
of the reports were of possible to highly probable certainty. Other reported
incident exposures included spills, stunted growth, discoloration, runoff,
persistence in crop and carryover.
'No effect (NE); May affect but not likely to adversely affect (NLAA); May affect and likely to adversely affect (LAA)
2 The LAA call is for all usese except Citrus and Potatoes. For both Citrus and Potatoes for both species (CRLF and AW), a
NLAA call was made by EFED. For Citrus and Potato, the LOC was exceeded for several indirect effects: (1) mammals as
prey (chronic, CRLF and AW), (2) birds as prey (acute, AW only), and (3) terrestrial plants (CRLF and AW). The reasons
for the NLAA calls are listed below:
Although the mammalian dose-based chronic LOC was exceeded for both the CRLF and the
AW prey, EFED determined that this effect would be insignificant as the potential small effect
on mammal reproduction (as prey of the CRLF and AW) would not likely impact the overall
prey base. It is anticipated that any effects would be small since the RQs only mildly exceeded
the LOC.
Although the avian acute dose-based LOC was exceeded for AW prey, EFED determined that
this effect was discountable and insignificant as the predicted percentage of acute effect was
only 0.0033% of the bird population (birds as prey items of the AW), and if even if this effect
did occur, the overall prey base of the AW would likely not be affected.
Although the terrestrial plant LOC was exceeded for both CRLF and the AW, EFED
determined the effect to be insignificant as the potential small effect on the vegetation would
likely not impact the overall habitat quality. It is anticipated that any effects would be small as
the RQs only mildly exceeded the LOC.
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Table 7.2 KITccls Dclorniin;ilion Siiiniiiiirv lor Critical llabilal Impact Analysis
Species
r.nripoinl
r.nw-is
l)clcrmin;ilion 1
ISiisis lor l)clcrmin;ilion
( Kl .1
Modilicalkiii of
aqualic-phase
I'Ci:
HM2
1 I'/.mi* l.( )('s were e\ceeded lor iiriikiciUs lorall modeled
scenarios except citrus and potatoes. LOCs were exceeded for dicots
for all modeled scenarios.
For 2,4-D, 358 incidents were reported for mostly plant damage to a
wide variety of terrestrial plants particularly from direct treatment or
spray drift. Other reported incident exposures included spills, stunted
growth, discoloration, runoff, persistence in crop and carryover. 140 of
these incidences are registered uses.
Non-vascular aquatic plants: LOC was exceeded for all direct surface
aquatic weed control scenarios.
Vascular aquatic plants: LOC was exceeded for several acid/salt use
scenarios and all direct application to water scenarios.
There is a potential for direct effects to aquatic-phase CRLF and
indirect effects via reduction of aquatic-phase prey items (aquatic
invertebrates, fish, and aquatic-phase amphibians) as described in
Section 5.
Modilicalkiii of
lerresl rial-phase
I'Ci:
HM2
Terrestrial plants: LOCs were exceeded for monocots for all modeled
scenarios except citrus and potatoes. LOCs were exceeded for dicots
for all modeled scenarios.
For 2,4-D, 358 incidents were reported for mostly plant damage to a
wide variety of terrestrial plants particularly from direct treatment or
spray drift. Other reported incident exposures included spills, stunted
growth, discoloration, runoff, persistence in crop and carryover. 140 of
these incidences are registered uses.
There is a potential for direct effects to terrestrial-phase CRLF and
indirect effects via reduction of terrestrial-phased prey items (mammals,
terrestrial invertebrates, and frogs) as described in Section 5.
\\\
Miidilicaluin of
lerresl rial-phase
pci :
HM2
Terrestrial plants: LOCs were exceeded for monocots for all modeled
scenarios except citrus and potatoes. LOCs were exceeded for dicots
for all modeled scenarios.
For 2,4-D, 358 incidents were reported for mostly plant damage to a
wide variety of terrestrial plants particularly from direct treatment or
spray drift. Other reported incident exposures included spills, stunted
growth, discoloration, runoff, persistence in crop and carryover. 140 of
these incidences are registered uses.
There is a potential for direct and indirect effects to the AW via
reduction of terrestrial-phased prey items (mammals, birds, terrestrial
invertebrates, and frogs) as described in Section 5.
habitat modification (HM) or No effect (NE)
2 The HM call is for all usese except Citrus and Potatoes. For both Citrus and Potatoes for both species (CRLF and AW), a
NE call was made by EFED. For Citrus and Potato, the LOC was exceeded for several indirect effects: (1) mammals as prey
(chronic, CRLF and AW), (2) birds as prey (acute, AW only), and (3) terrestrial plants (CRLF and AW). The reasons for
the NE calls are listed below:
Although the mammalian dose-based chronic LOC was exceeded for both the CRLF and the
AW prey, EFED determined that this effect would be insignificant as the potential small effect
179
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on mammal reproduction (as prey of the CRLF and AW) would not likely impact the overall
prey base. It is anticipated that any effects would be small since the RQs only mildly exceeded
the LOC.
Although the avian acute dose-based LOC was exceeded for AW prey, EFED determined that
this effect was discountable and insignificant as the predicted percentage of acute effect was
only 0.0033% of the bird population (birds as prey items of the AW), and if even if this effect
did occur, the overall prey base of the AW would likely not be affected.
Although the terrestrial plant LOC was exceeded for both CRLF and the AW, EFED
determined the effect to be insignificant as the potential small effect on the vegetation would
likely not impact the overall habitat quality. It is anticipated that any effects would be small as
the RQs only mildly exceeded the LOC.
Based on the conclusions of this assessment, a formal consultation with the U. S. Fish
and Wildlife Service under Section 7 of the Endangered Species Act should be initiated.
When evaluating the significance of this risk assessment's direct/indirect and adverse
habitat modification effects determinations, it is important to note that pesticide
exposures and predicted risks to the species and its resources {i.e., food and habitat) are
not expected to be uniform across the action area. In fact, given the assumptions of drift
and downstream transport {i.e., attenuation with distance), pesticide exposure and
associated risks to the species and its resources are expected to decrease with increasing
distance away from the treated field or site of application. Evaluation of the implication
of this non-uniform distribution of risk to the species would require information and
assessment techniques that are not currently available. Examples of such information and
methodology required for this type of analysis would include the following:
Enhanced information on the density and distribution of CRLF and AW
life stages within the action area and/or applicable designated critical
habitat. This information would allow for quantitative extrapolation of the
present risk assessment's predictions of individual effects to the
proportion of the population extant within geographical areas where those
effects are predicted. Furthermore, such population information would
allow for a more comprehensive evaluation of the significance of potential
resource impairment to individuals of the assessed species.
Quantitative information on prey base requirements for the assessed
species. While existing information provides a preliminary picture of the
types of food sources utilized by the assessed species, it does not establish
minimal requirements to sustain healthy individuals at varying life stages.
Such information could be used to establish biologically relevant
thresholds of effects on the prey base, and ultimately establish
geographical limits to those effects. This information could be used
together with the density data discussed above to characterize the
likelihood of adverse effects to individuals.
Information on population responses of prey base organisms to the
pesticide. Currently, methodologies are limited to predicting exposures
and likely levels of direct mortality, growth or reproductive impairment
180
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immediately following exposure to the pesticide. The degree to which
repeated exposure events and the inherent demographic characteristics of
the prey population play into the extent to which prey resources may
recover is not predictable. An enhanced understanding of long-term prey
responses to pesticide exposure would allow for a more refined
determination of the magnitude and duration of resource impairment, and
together with the information described above, a more complete prediction
of effects to individual species and potential modification to critical
habitat.
8. References
Anderson, A.M, Byrtus, G., Thompson J., Humphries, D., Hill, B., and Bilyk, M., 2002.
Baseline Pesticide Data for Semi-Permanent Wetlands in the Aspen Parkland of
Alberta. Albeta Environment, Publication No. T/673.
Feitshans, T.A., 1999. An Analysis of State Pesticide Drift Laws, San Joaquin Agric. L.
Rev. 1, 37 (Spring 1999).
Fletcher, J.S., J.E. Nellessen, and T.G. Pfleeger. 1994. Literature review and evaluation
of the EPA food-chain (Kenaga) nomogram, and instrument for estimating
pesticide residues on plants. Environmental Toxicology and Chemistry 13
(9): 1383-1391.
Gibson, L. R. and M. Liebman. 2002. Course Material tor Principles of Weed Science,
Agronomy 317, Iowa State University. Website accessed 15 July 2003,
http://www.agron.iastate.edu/courses/Agron317/Herbicide mode of action.htm.
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